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Allow exporting vmlinux debuginfo #11

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Merged
merged 3 commits into from
Nov 18, 2020
Merged

Allow exporting vmlinux debuginfo #11

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854de8b
Do not skip segments of type SEG_CODE
mephi42 Oct 18, 2019
8846a7c
Skip segments without functions
mephi42 Oct 14, 2020
db9d4d4
Allow overlapping sections
mephi42 Oct 14, 2020
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5 changes: 3 additions & 2 deletions src/dwarfexport.cpp
100644 → 100755
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Original file line number Diff line number Diff line change
Expand Up @@ -724,7 +724,7 @@ void add_debug_info(std::shared_ptr<DwarfGenInfo> info,

// Only consider EXEC segments
// TODO: Skip plt/got?
if (!(seg->perm & SEGPERM_EXEC)) {
if (!(seg->perm & SEGPERM_EXEC) && seg->type != SEG_CODE) {
dwarfexport_log("Segment #", segn, " is not executable. Skipping.");
continue;
}
Expand All @@ -740,7 +740,8 @@ void add_debug_info(std::shared_ptr<DwarfGenInfo> info,
f = get_next_func(seg->startEA);

if (f == nullptr) {
dwarfexport_error("get_next_func() failed");
dwarfexport_log("Skipping ", lsegname, " because it has no functions");
continue;
}
}

Expand Down
52 changes: 47 additions & 5 deletions src/dwarfgen.cpp
100644 → 100755
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Original file line number Diff line number Diff line change
Expand Up @@ -144,7 +144,7 @@ std::shared_ptr<DwarfGenInfo> generate_dwarf_object(const Options &options) {
}

static Elf_Scn *get_last_section(Elf *elf) {
std::size_t count, max_offset = 0;
std::size_t count, max_offset = 0, max_size = 0;
GElf_Shdr shdr;
Elf_Scn *last_scn;

Expand All @@ -156,9 +156,14 @@ static Elf_Scn *get_last_section(Elf *elf) {
if (!gelf_getshdr(scn, &shdr)) {
dwarfexport_error("elf_getshdr() failed: ", elf_errmsg(-1));
}
if (shdr.sh_offset > max_offset) {
if (shdr.sh_type == SHT_NOBITS) {
continue;
}
if (shdr.sh_offset > max_offset ||
(shdr.sh_offset == max_offset && shdr.sh_size > max_size)) {
last_scn = scn;
max_offset = shdr.sh_offset;
max_size = shdr.sh_size;
}
}
return last_scn;
Expand Down Expand Up @@ -243,6 +248,34 @@ static void add_debug_section_data(std::shared_ptr<DwarfGenInfo> info) {
}
}

static void log_elf(Elf *elf) {
GElf_Ehdr ehdr;
int scn_index;
Elf_Scn *scn;
GElf_Shdr shdr;

if (gelf_getehdr(elf, &ehdr) != &ehdr)
dwarfexport_error("gelf_getehdr() failed: ", elf_errmsg(-1));

for (scn_index = 1; scn_index < ehdr.e_shnum; scn_index++) {
if ((scn = elf_getscn(elf, scn_index)) == NULL)
dwarfexport_error("getshdr() failed: ", elf_errmsg(-1));
if (gelf_getshdr(scn, &shdr) != &shdr)
dwarfexport_error("getshdr() failed: ", elf_errmsg(-1));
dwarfexport_log("Section #", scn_index,
": sh_name=", shdr.sh_name,
", sh_type=", shdr.sh_type,
", sh_flags=", shdr.sh_flags,
", sh_addr=", shdr.sh_addr,
", sh_offset=", shdr.sh_offset,
", sh_size=", shdr.sh_size,
", sh_link=", shdr.sh_link,
", sh_info=", shdr.sh_info,
", sh_addralign=", shdr.sh_addralign,
", sh_entsize=", shdr.sh_entsize);
}
}

static void generate_copy_with_dbg_info(std::shared_ptr<DwarfGenInfo> info,
const std::string &src,
const std::string &dst) {
Expand Down Expand Up @@ -284,10 +317,10 @@ static void generate_copy_with_dbg_info(std::shared_ptr<DwarfGenInfo> info,

info->elf = elf_out;

/* Some compilers produce binaries with non-adjacent sections, so
* we cannot use the automatic layout. Suppress it and use the exact
/* Some compilers produce binaries with non-adjacent or overlapping sections,
* so we cannot use the automatic layout. Suppress it and use the exact
* layout from the input. */
if (elf_flagelf(elf_out, ELF_C_SET, ELF_F_LAYOUT) == 0)
if (elf_flagelf(elf_out, ELF_C_SET, ELF_F_LAYOUT | ELF_F_LAYOUT_OVERLAP) == 0)
dwarfexport_error("elf_flagelf failed: ", elf_errmsg(-1));

if (gelf_getehdr(elf_out, &ehdr_out) != &ehdr_out)
Expand Down Expand Up @@ -346,8 +379,14 @@ static void generate_copy_with_dbg_info(std::shared_ptr<DwarfGenInfo> info,
dwarfexport_error("gelf_update_shdr() failed: ", elf_errmsg(-1));
}

dwarfexport_log("After copying the original sections:");
log_elf(elf_out);

add_debug_section_data(info);

dwarfexport_log("After adding the debug sections:");
log_elf(elf_out);

// Get the current last section (to fix section header and string table loc)
auto last_scn = get_last_section(elf_out);
GElf_Shdr last_shdr;
Expand All @@ -374,6 +413,9 @@ static void generate_copy_with_dbg_info(std::shared_ptr<DwarfGenInfo> info,
if (gelf_update_ehdr(elf_out, &ehdr_out) == 0)
dwarfexport_error("gelf_update_ehdr() failed: ", elf_errmsg(-1));

dwarfexport_log("After fixing various offsets:");
log_elf(elf_out);

if (elf_update(elf_out, ELF_C_WRITE) < 0)
dwarfexport_error("elf_update() failed: ", elf_errmsg(-1));

Expand Down