mesa/src/amd/common/ac_rtld.c

/*
 * Copyright 2014-2019 Advanced Micro Devices, Inc.
 *
 * SPDX-License-Identifier: MIT
 */

#include "ac_rtld.h"

#include "ac_binary.h"
#include "ac_gpu_info.h"
#include "util/compiler.h"
#include "util/u_dynarray.h"
#include "util/u_math.h"

#include <gelf.h>
#include <libelf.h>
#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#ifndef EM_AMDGPU
// Old distributions may not have this enum constant
#define EM_AMDGPU 224
#endif

#ifndef STT_AMDGPU_LDS
#define STT_AMDGPU_LDS 13 // this is deprecated -- remove
#endif

#ifndef SHN_AMDGPU_LDS
#define SHN_AMDGPU_LDS 0xff00
#endif

#ifndef R_AMDGPU_NONE
#define R_AMDGPU_NONE          0
#define R_AMDGPU_ABS32_LO      1
#define R_AMDGPU_ABS32_HI      2
#define R_AMDGPU_ABS64         3
#define R_AMDGPU_REL32         4
#define R_AMDGPU_REL64         5
#define R_AMDGPU_ABS32         6
#define R_AMDGPU_GOTPCREL      7
#define R_AMDGPU_GOTPCREL32_LO 8
#define R_AMDGPU_GOTPCREL32_HI 9
#define R_AMDGPU_REL32_LO      10
#define R_AMDGPU_REL32_HI      11
#define R_AMDGPU_RELATIVE64    13
#endif

/* For the UMR disassembler. */
#define DEBUGGER_END_OF_CODE_MARKER 0xbf9f0000 /* invalid instruction */
#define DEBUGGER_NUM_MARKERS        5

struct ac_rtld_section {
   bool is_rx : 1;
   bool is_pasted_text : 1;
   uint64_t offset;
   const char *name;
};

struct ac_rtld_part {
   Elf *elf;
   struct ac_rtld_section *sections;
   unsigned num_sections;
};

static void report_errorvf(const char *fmt, va_list va)
{
   fprintf(stderr, "ac_rtld error: ");

   vfprintf(stderr, fmt, va);

   fprintf(stderr, "\n");
}

static void report_errorf(const char *fmt, ...) PRINTFLIKE(1, 2);

static void report_errorf(const char *fmt, ...)
{
   va_list va;
   va_start(va, fmt);
   report_errorvf(fmt, va);
   va_end(va);
}

static void report_elf_errorf(const char *fmt, ...) PRINTFLIKE(1, 2);

static void report_elf_errorf(const char *fmt, ...)
{
   va_list va;
   va_start(va, fmt);
   report_errorvf(fmt, va);
   va_end(va);

   fprintf(stderr, "ELF error: %s\n", elf_errmsg(elf_errno()));
}

/**
 * Find a symbol in a dynarray of struct ac_rtld_symbol by \p name and shader
 * \p part_idx.
 */
static const struct ac_rtld_symbol *find_symbol(const struct util_dynarray *symbols,
                                                const char *name, unsigned part_idx)
{
   util_dynarray_foreach (symbols, struct ac_rtld_symbol, symbol) {
      if ((symbol->part_idx == ~0u || symbol->part_idx == part_idx) && !strcmp(name, symbol->name))
         return symbol;
   }
   return NULL;
}

static int compare_symbol_by_align(const void *lhsp, const void *rhsp)
{
   const struct ac_rtld_symbol *lhs = lhsp;
   const struct ac_rtld_symbol *rhs = rhsp;
   if (rhs->align > lhs->align)
      return 1;
   if (rhs->align < lhs->align)
      return -1;
   return 0;
}

/**
 * Sort the given symbol list by decreasing alignment and assign offsets.
 */
static bool layout_symbols(struct ac_rtld_symbol *symbols, unsigned num_symbols,
                           uint64_t *ptotal_size)
{
   qsort(symbols, num_symbols, sizeof(*symbols), compare_symbol_by_align);

   uint64_t total_size = *ptotal_size;

   for (unsigned i = 0; i < num_symbols; ++i) {
      struct ac_rtld_symbol *s = &symbols[i];
      assert(util_is_power_of_two_nonzero(s->align));

      total_size = align64(total_size, s->align);
      s->offset = total_size;

      if (total_size + s->size < total_size) {
         report_errorf("%s: size overflow", __func__);
         return false;
      }

      total_size += s->size;
   }

   *ptotal_size = total_size;
   return true;
}

/**
 * Read LDS symbols from the given \p section of the ELF of \p part and append
 * them to the LDS symbols list.
 *
 * Shared LDS symbols are filtered out.
 */
static bool read_private_lds_symbols(struct ac_rtld_binary *binary, unsigned part_idx,
                                     Elf_Scn *section, uint32_t *lds_end_align)
{
#define report_if(cond)                                                                            \
   do {                                                                                            \
      if ((cond)) {                                                                                \
         report_errorf(#cond);                                                                     \
         return false;                                                                             \
      }                                                                                            \
   } while (false)
#define report_elf_if(cond)                                                                        \
   do {                                                                                            \
      if ((cond)) {                                                                                \
         report_elf_errorf(#cond);                                                                 \
         return false;                                                                             \
      }                                                                                            \
   } while (false)

   struct ac_rtld_part *part = &binary->parts[part_idx];
   Elf64_Shdr *shdr = elf64_getshdr(section);
   uint32_t strtabidx = shdr->sh_link;
   Elf_Data *symbols_data = elf_getdata(section, NULL);
   report_elf_if(!symbols_data);

   const Elf64_Sym *symbol = symbols_data->d_buf;
   size_t num_symbols = symbols_data->d_size / sizeof(Elf64_Sym);

   for (size_t j = 0; j < num_symbols; ++j, ++symbol) {
      struct ac_rtld_symbol s = {0};

      if (ELF64_ST_TYPE(symbol->st_info) == STT_AMDGPU_LDS) {
         /* old-style LDS symbols from initial prototype -- remove eventually */
         s.align = MIN2(1u << (symbol->st_other >> 3), 1u << 16);
      } else if (symbol->st_shndx == SHN_AMDGPU_LDS) {
         s.align = MIN2(symbol->st_value, 1u << 16);
         report_if(!util_is_power_of_two_nonzero(s.align));
      } else
         continue;

      report_if(symbol->st_size > 1u << 29);

      s.name = elf_strptr(part->elf, strtabidx, symbol->st_name);
      s.size = symbol->st_size;
      s.part_idx = part_idx;

      if (!strcmp(s.name, "__lds_end")) {
         report_elf_if(s.size != 0);
         *lds_end_align = MAX2(*lds_end_align, s.align);
         continue;
      }

      const struct ac_rtld_symbol *shared = find_symbol(&binary->lds_symbols, s.name, part_idx);
      if (shared) {
         report_elf_if(s.align > shared->align);
         report_elf_if(s.size > shared->size);
         continue;
      }

      util_dynarray_append(&binary->lds_symbols, struct ac_rtld_symbol, s);
   }

   return true;

#undef report_if
#undef report_elf_if
}

/**
 * Open a binary consisting of one or more shader parts.
 *
 * \param binary the uninitialized struct
 * \param i binary opening parameters
 */
bool ac_rtld_open(struct ac_rtld_binary *binary, struct ac_rtld_open_info i)
{
   /* One of the libelf implementations
    * (http://www.mr511.de/software/english.htm) requires calling
    * elf_version() before elf_memory().
    */
   elf_version(EV_CURRENT);

   memset(binary, 0, sizeof(*binary));
   memcpy(&binary->options, &i.options, sizeof(binary->options));
   binary->wave_size = i.wave_size;
   binary->gfx_level = i.info->gfx_level;
   binary->num_parts = i.num_parts;
   binary->parts = calloc(sizeof(*binary->parts), i.num_parts);
   if (!binary->parts)
      return false;

   uint64_t pasted_text_size = 0;
   uint64_t rx_align = 1;
   uint64_t rx_size = 0;
   uint64_t exec_size = 0;

#define report_if(cond)                                                                            \
   do {                                                                                            \
      if ((cond)) {                                                                                \
         report_errorf(#cond);                                                                     \
         goto fail;                                                                                \
      }                                                                                            \
   } while (false)
#define report_elf_if(cond)                                                                        \
   do {                                                                                            \
      if ((cond)) {                                                                                \
         report_elf_errorf(#cond);                                                                 \
         goto fail;                                                                                \
      }                                                                                            \
   } while (false)

   /* Copy and layout shared LDS symbols. */
   if (i.num_shared_lds_symbols) {
      if (!util_dynarray_resize(&binary->lds_symbols, struct ac_rtld_symbol,
                                i.num_shared_lds_symbols))
         goto fail;

      memcpy(binary->lds_symbols.data, i.shared_lds_symbols, binary->lds_symbols.size);
   }

   util_dynarray_foreach (&binary->lds_symbols, struct ac_rtld_symbol, symbol)
      symbol->part_idx = ~0u;

   unsigned max_lds_size = i.info->gfx_level == GFX6 ? 32 * 1024 : 64 * 1024;

   uint64_t shared_lds_size = 0;
   if (!layout_symbols(binary->lds_symbols.data, i.num_shared_lds_symbols, &shared_lds_size))
      goto fail;

   if (shared_lds_size > max_lds_size) {
      fprintf(stderr, "ac_rtld error(1): too much LDS (used = %u, max = %u)\n",
              (unsigned)shared_lds_size, max_lds_size);
      goto fail;
   }
   binary->lds_size = shared_lds_size;

   /* First pass over all parts: open ELFs, pre-determine the placement of
    * sections in the memory image, and collect and layout private LDS symbols. */
   uint32_t lds_end_align = 0;

   if (binary->options.halt_at_entry)
      pasted_text_size += 4;

   for (unsigned part_idx = 0; part_idx < i.num_parts; ++part_idx) {
      struct ac_rtld_part *part = &binary->parts[part_idx];
      unsigned part_lds_symbols_begin =
         util_dynarray_num_elements(&binary->lds_symbols, struct ac_rtld_symbol);

      part->elf = elf_memory((char *)i.elf_ptrs[part_idx], i.elf_sizes[part_idx]);
      report_elf_if(!part->elf);

      const Elf64_Ehdr *ehdr = elf64_getehdr(part->elf);
      report_elf_if(!ehdr);
      report_if(ehdr->e_machine != EM_AMDGPU);

      size_t section_str_index;
      size_t num_shdrs;
      report_elf_if(elf_getshdrstrndx(part->elf, &section_str_index) < 0);
      report_elf_if(elf_getshdrnum(part->elf, &num_shdrs) < 0);

      part->num_sections = num_shdrs;
      part->sections = calloc(sizeof(*part->sections), num_shdrs);
      report_if(!part->sections);

      Elf_Scn *section = NULL;
      while ((section = elf_nextscn(part->elf, section))) {
         Elf64_Shdr *shdr = elf64_getshdr(section);
         struct ac_rtld_section *s = &part->sections[elf_ndxscn(section)];
         s->name = elf_strptr(part->elf, section_str_index, shdr->sh_name);
         report_elf_if(!s->name);

         /* Cannot actually handle linked objects yet */
         report_elf_if(shdr->sh_addr != 0);

         /* Alignment must be 0 or a power of two */
         report_elf_if(shdr->sh_addralign & (shdr->sh_addralign - 1));
         uint64_t sh_align = MAX2(shdr->sh_addralign, 1);

         if (shdr->sh_flags & SHF_ALLOC && shdr->sh_type != SHT_NOTE) {
            report_if(shdr->sh_flags & SHF_WRITE);

            s->is_rx = true;

            if (shdr->sh_flags & SHF_EXECINSTR) {
               report_elf_if(shdr->sh_size & 3);

               if (!strcmp(s->name, ".text"))
                  s->is_pasted_text = true;

               exec_size += shdr->sh_size;
            }

            if (s->is_pasted_text) {
               s->offset = pasted_text_size;
               pasted_text_size += shdr->sh_size;
            } else {
               rx_align = align(rx_align, sh_align);
               rx_size = align(rx_size, sh_align);
               s->offset = rx_size;
               rx_size += shdr->sh_size;
            }
         } else if (shdr->sh_type == SHT_SYMTAB) {
            if (!read_private_lds_symbols(binary, part_idx, section, &lds_end_align))
               goto fail;
         }
      }

      uint64_t part_lds_size = shared_lds_size;
      if (!layout_symbols(util_dynarray_element(&binary->lds_symbols, struct ac_rtld_symbol,
                                                part_lds_symbols_begin),
                          util_dynarray_num_elements(&binary->lds_symbols, struct ac_rtld_symbol) -
                             part_lds_symbols_begin,
                          &part_lds_size))
         goto fail;
      binary->lds_size = MAX2(binary->lds_size, part_lds_size);
   }

   binary->rx_end_markers = pasted_text_size;
   pasted_text_size += 4 * DEBUGGER_NUM_MARKERS;

   /* __lds_end is a special symbol that points at the end of the memory
    * occupied by other LDS symbols. Its alignment is taken as the
    * maximum of its alignment over all shader parts where it occurs.
    */
   if (lds_end_align) {
      binary->lds_size = align(binary->lds_size, lds_end_align);

      struct ac_rtld_symbol *lds_end =
         util_dynarray_grow(&binary->lds_symbols, struct ac_rtld_symbol, 1);
      lds_end->name = "__lds_end";
      lds_end->size = 0;
      lds_end->align = lds_end_align;
      lds_end->offset = binary->lds_size;
      lds_end->part_idx = ~0u;
   }

   if (binary->lds_size > max_lds_size) {
      fprintf(stderr, "ac_rtld error(2): too much LDS (used = %u, max = %u)\n",
              (unsigned)binary->lds_size, max_lds_size);
      goto fail;
   }

   /* Second pass: Adjust offsets of non-pasted text sections. */
   binary->rx_size = pasted_text_size;
   binary->rx_size = align(binary->rx_size, rx_align);

   for (unsigned part_idx = 0; part_idx < i.num_parts; ++part_idx) {
      struct ac_rtld_part *part = &binary->parts[part_idx];
      size_t num_shdrs;
      elf_getshdrnum(part->elf, &num_shdrs);

      for (unsigned j = 0; j < num_shdrs; ++j) {
         struct ac_rtld_section *s = &part->sections[j];
         if (s->is_rx && !s->is_pasted_text)
            s->offset += binary->rx_size;
      }
   }

   binary->rx_size += rx_size;
   binary->exec_size = exec_size;

   binary->rx_size = ac_align_shader_binary_for_prefetch(i.info, binary->rx_size);

   return true;

#undef report_if
#undef report_elf_if

fail:
   ac_rtld_close(binary);
   return false;
}

void ac_rtld_close(struct ac_rtld_binary *binary)
{
   for (unsigned i = 0; i < binary->num_parts; ++i) {
      struct ac_rtld_part *part = &binary->parts[i];
      free(part->sections);
      elf_end(part->elf);
   }

   util_dynarray_fini(&binary->lds_symbols);
   free(binary->parts);
   binary->parts = NULL;
   binary->num_parts = 0;
}

static bool get_section_by_name(struct ac_rtld_part *part, const char *name, const char **data,
                                size_t *nbytes)
{
   for (unsigned i = 0; i < part->num_sections; ++i) {
      struct ac_rtld_section *s = &part->sections[i];
      if (s->name && !strcmp(name, s->name)) {
         Elf_Scn *target_scn = elf_getscn(part->elf, i);
         Elf_Data *target_data = elf_getdata(target_scn, NULL);
         if (!target_data) {
            report_elf_errorf("ac_rtld: get_section_by_name: elf_getdata");
            return false;
         }

         *data = target_data->d_buf;
         *nbytes = target_data->d_size;
         return true;
      }
   }
   return false;
}

bool ac_rtld_get_section_by_name(struct ac_rtld_binary *binary, const char *name, const char **data,
                                 size_t *nbytes)
{
   assert(binary->num_parts == 1);
   return get_section_by_name(&binary->parts[0], name, data, nbytes);
}

bool ac_rtld_read_config(const struct radeon_info *info, struct ac_rtld_binary *binary,
                         struct ac_shader_config *config)
{
   for (unsigned i = 0; i < binary->num_parts; ++i) {
      struct ac_rtld_part *part = &binary->parts[i];
      const char *config_data;
      size_t config_nbytes;

      if (!get_section_by_name(part, ".AMDGPU.config", &config_data, &config_nbytes))
         return false;

      /* TODO: be precise about scratch use? */
      struct ac_shader_config c = {0};
      ac_parse_shader_binary_config(config_data, config_nbytes, binary->wave_size, info, &c);

      config->num_sgprs = MAX2(config->num_sgprs, c.num_sgprs);
      config->num_vgprs = MAX2(config->num_vgprs, c.num_vgprs);
      config->spilled_sgprs = MAX2(config->spilled_sgprs, c.spilled_sgprs);
      config->spilled_vgprs = MAX2(config->spilled_vgprs, c.spilled_vgprs);
      config->scratch_bytes_per_wave =
         MAX2(config->scratch_bytes_per_wave, c.scratch_bytes_per_wave);

      assert(i == 0 || config->float_mode == c.float_mode);
      config->float_mode = c.float_mode;

      /* SPI_PS_INPUT_ENA/ADDR can't be combined. Only the value from
       * the main shader part is used. */
      assert(config->spi_ps_input_ena == 0 && config->spi_ps_input_addr == 0);
      config->spi_ps_input_ena = c.spi_ps_input_ena;
      config->spi_ps_input_addr = c.spi_ps_input_addr;

      /* TODO: consistently use LDS symbols for this */
      config->lds_size = MAX2(config->lds_size, c.lds_size);

      /* TODO: Should we combine these somehow? It's currently only
       * used for radeonsi's compute, where multiple parts aren't used. */
      assert(config->rsrc1 == 0 && config->rsrc2 == 0);
      config->rsrc1 = c.rsrc1;
      config->rsrc2 = c.rsrc2;
   }

   return true;
}

static bool resolve_symbol(const struct ac_rtld_upload_info *u, unsigned part_idx,
                           const Elf64_Sym *sym, const char *name, uint64_t *value)
{
   /* TODO: properly disentangle the undef and the LDS cases once
    * STT_AMDGPU_LDS is retired. */
   if (sym->st_shndx == SHN_UNDEF || sym->st_shndx == SHN_AMDGPU_LDS) {
      const struct ac_rtld_symbol *lds_sym = find_symbol(&u->binary->lds_symbols, name, part_idx);

      if (lds_sym) {
         *value = lds_sym->offset;
         return true;
      }

      /* TODO: resolve from other parts */

      if (u->get_external_symbol(u->binary->gfx_level, u->cb_data, name, value))
         return true;

      report_errorf("symbol %s: unknown", name);
      return false;
   }

   struct ac_rtld_part *part = &u->binary->parts[part_idx];
   if (sym->st_shndx >= part->num_sections) {
      report_errorf("symbol %s: section out of bounds", name);
      return false;
   }

   struct ac_rtld_section *s = &part->sections[sym->st_shndx];
   if (!s->is_rx) {
      report_errorf("symbol %s: bad section", name);
      return false;
   }

   uint64_t section_base = u->rx_va + s->offset;

   *value = section_base + sym->st_value;
   return true;
}

static bool apply_relocs(const struct ac_rtld_upload_info *u, unsigned part_idx,
                         const Elf64_Shdr *reloc_shdr, const Elf_Data *reloc_data)
{
#define report_if(cond)                                                                            \
   do {                                                                                            \
      if ((cond)) {                                                                                \
         report_errorf(#cond);                                                                     \
         return false;                                                                             \
      }                                                                                            \
   } while (false)
#define report_elf_if(cond)                                                                        \
   do {                                                                                            \
      if ((cond)) {                                                                                \
         report_elf_errorf(#cond);                                                                 \
         return false;                                                                             \
      }                                                                                            \
   } while (false)

   struct ac_rtld_part *part = &u->binary->parts[part_idx];
   Elf_Scn *target_scn = elf_getscn(part->elf, reloc_shdr->sh_info);
   report_elf_if(!target_scn);

   Elf_Data *target_data = elf_getdata(target_scn, NULL);
   report_elf_if(!target_data);

   Elf_Scn *symbols_scn = elf_getscn(part->elf, reloc_shdr->sh_link);
   report_elf_if(!symbols_scn);

   Elf64_Shdr *symbols_shdr = elf64_getshdr(symbols_scn);
   report_elf_if(!symbols_shdr);
   uint32_t strtabidx = symbols_shdr->sh_link;

   Elf_Data *symbols_data = elf_getdata(symbols_scn, NULL);
   report_elf_if(!symbols_data);

   const Elf64_Sym *symbols = symbols_data->d_buf;
   size_t num_symbols = symbols_data->d_size / sizeof(Elf64_Sym);

   struct ac_rtld_section *s = &part->sections[reloc_shdr->sh_info];
   report_if(!s->is_rx);

   const char *orig_base = target_data->d_buf;
   char *dst_base = u->rx_ptr + s->offset;
   uint64_t va_base = u->rx_va + s->offset;

   Elf64_Rel *rel = reloc_data->d_buf;
   size_t num_relocs = reloc_data->d_size / sizeof(*rel);
   for (size_t i = 0; i < num_relocs; ++i, ++rel) {
      size_t r_sym = ELF64_R_SYM(rel->r_info);
      unsigned r_type = ELF64_R_TYPE(rel->r_info);

      const char *orig_ptr = orig_base + rel->r_offset;
      char *dst_ptr = dst_base + rel->r_offset;
      uint64_t va = va_base + rel->r_offset;

      uint64_t symbol;
      uint64_t addend;

      if (r_sym == STN_UNDEF) {
         symbol = 0;
      } else {
         report_elf_if(r_sym >= num_symbols);

         const Elf64_Sym *sym = &symbols[r_sym];
         const char *symbol_name = elf_strptr(part->elf, strtabidx, sym->st_name);
         report_elf_if(!symbol_name);

         if (!resolve_symbol(u, part_idx, sym, symbol_name, &symbol))
            return false;
      }

      /* TODO: Should we also support .rela sections, where the
       * addend is part of the relocation record? */

      /* Load the addend from the ELF instead of the destination,
       * because the destination may be in VRAM. */
      switch (r_type) {
      case R_AMDGPU_ABS32:
      case R_AMDGPU_ABS32_LO:
      case R_AMDGPU_ABS32_HI:
      case R_AMDGPU_REL32:
      case R_AMDGPU_REL32_LO:
      case R_AMDGPU_REL32_HI:
         addend = *(const uint32_t *)orig_ptr;
         break;
      case R_AMDGPU_ABS64:
      case R_AMDGPU_REL64:
         addend = *(const uint64_t *)orig_ptr;
         break;
      default:
         report_errorf("unsupported r_type == %u", r_type);
         return false;
      }

      uint64_t abs = symbol + addend;

      switch (r_type) {
      case R_AMDGPU_ABS32:
         assert((uint32_t)abs == abs);
         FALLTHROUGH;
      case R_AMDGPU_ABS32_LO:
         *(uint32_t *)dst_ptr = util_cpu_to_le32(abs);
         break;
      case R_AMDGPU_ABS32_HI:
         *(uint32_t *)dst_ptr = util_cpu_to_le32(abs >> 32);
         break;
      case R_AMDGPU_ABS64:
         *(uint64_t *)dst_ptr = util_cpu_to_le64(abs);
         break;
      case R_AMDGPU_REL32:
         assert((int64_t)(int32_t)(abs - va) == (int64_t)(abs - va));
         FALLTHROUGH;
      case R_AMDGPU_REL32_LO:
         *(uint32_t *)dst_ptr = util_cpu_to_le32(abs - va);
         break;
      case R_AMDGPU_REL32_HI:
         *(uint32_t *)dst_ptr = util_cpu_to_le32((abs - va) >> 32);
         break;
      case R_AMDGPU_REL64:
         *(uint64_t *)dst_ptr = util_cpu_to_le64(abs - va);
         break;
      default:
         unreachable("bad r_type");
      }
   }

   return true;

#undef report_if
#undef report_elf_if
}

/**
 * Upload the binary or binaries to the provided GPU buffers, including
 * relocations.
 */
int ac_rtld_upload(struct ac_rtld_upload_info *u)
{
#define report_if(cond)                                                                            \
   do {                                                                                            \
      if ((cond)) {                                                                                \
         report_errorf(#cond);                                                                     \
         return -1;                                                                             \
      }                                                                                            \
   } while (false)
#define report_elf_if(cond)                                                                        \
   do {                                                                                            \
      if ((cond)) {                                                                                \
         report_errorf(#cond);                                                                     \
         return -1;                                                                             \
      }                                                                                            \
   } while (false)

   int size = 0;
   if (u->binary->options.halt_at_entry) {
      /* s_sethalt 1 */
      *(uint32_t *)u->rx_ptr = util_cpu_to_le32(0xbf8d0001);
   }

   /* First pass: upload raw section data and lay out private LDS symbols. */
   for (unsigned i = 0; i < u->binary->num_parts; ++i) {
      struct ac_rtld_part *part = &u->binary->parts[i];

      Elf_Scn *section = NULL;
      while ((section = elf_nextscn(part->elf, section))) {
         Elf64_Shdr *shdr = elf64_getshdr(section);
         struct ac_rtld_section *s = &part->sections[elf_ndxscn(section)];

         if (!s->is_rx)
            continue;

         report_if(shdr->sh_type != SHT_PROGBITS);

         Elf_Data *data = elf_getdata(section, NULL);
         report_elf_if(!data || data->d_size != shdr->sh_size);
         memcpy(u->rx_ptr + s->offset, data->d_buf, shdr->sh_size);

         size = MAX2(size, s->offset + shdr->sh_size);
      }
   }

   if (u->binary->rx_end_markers) {
      uint32_t *dst = (uint32_t *)(u->rx_ptr + u->binary->rx_end_markers);
      for (unsigned i = 0; i < DEBUGGER_NUM_MARKERS; ++i)
         *dst++ = util_cpu_to_le32(DEBUGGER_END_OF_CODE_MARKER);
      size += 4 * DEBUGGER_NUM_MARKERS;
   }

   /* Second pass: handle relocations, overwriting uploaded data where
    * appropriate. */
   for (unsigned i = 0; i < u->binary->num_parts; ++i) {
      struct ac_rtld_part *part = &u->binary->parts[i];
      Elf_Scn *section = NULL;
      while ((section = elf_nextscn(part->elf, section))) {
         Elf64_Shdr *shdr = elf64_getshdr(section);
         if (shdr->sh_type == SHT_REL) {
            Elf_Data *relocs = elf_getdata(section, NULL);
            report_elf_if(!relocs || relocs->d_size != shdr->sh_size);
            if (!apply_relocs(u, i, shdr, relocs))
               return -1;
         } else if (shdr->sh_type == SHT_RELA) {
            report_errorf("SHT_RELA not supported");
            return -1;
         }
      }
   }

   return size;

#undef report_if
#undef report_elf_if
}