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Fix assertion failure when setting the interpreter of a debug-only executable #595

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Fix assertion failure when setting the interpreter of a debug-only executable #595

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81f59ad
Add test for setting interpreter on debug-only executable
corngood Apr 20, 2025
dbcbded
Skip NOBITS sections when finding start of executable rewrite
corngood Apr 20, 2025
ad3d3d4
Skip rewrite of SHT_NOBITS .dynamic section
corngood Apr 21, 2025
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14 changes: 8 additions & 6 deletions src/patchelf.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -997,9 +997,6 @@ void ElfFile<ElfFileParamNames>::rewriteSectionsExecutable()
Stop when we reach an irreplacable section (such as one of type
SHT_PROGBITS). These cannot be moved in virtual address space
since that would invalidate absolute references to them. */
assert(lastReplaced + 1 < shdrs.size()); /* !!! I'm lazy. */
size_t startOffset = rdi(shdrs.at(lastReplaced + 1).sh_offset);
Elf_Addr startAddr = rdi(shdrs.at(lastReplaced + 1).sh_addr);
std::string prevSection;
for (unsigned int i = 1; i <= lastReplaced; ++i) {
Elf_Shdr & shdr(shdrs.at(i));
Expand All @@ -1010,8 +1007,6 @@ void ElfFile<ElfFileParamNames>::rewriteSectionsExecutable()
if ((rdi(shdr.sh_type) == SHT_PROGBITS && sectionName != ".interp")
|| prevSection == ".dynstr")
{
startOffset = rdi(shdr.sh_offset);
startAddr = rdi(shdr.sh_addr);
lastReplaced = i - 1;
break;
}
Expand All @@ -1022,6 +1017,13 @@ void ElfFile<ElfFileParamNames>::rewriteSectionsExecutable()
prevSection = std::move(sectionName);
}

while (lastReplaced < shdrs.size() && shdrs.at(lastReplaced).sh_type == SHT_NOBITS)
++lastReplaced;

assert(lastReplaced + 1 < shdrs.size()); /* !!! I'm lazy. */
size_t startOffset = rdi(shdrs.at(lastReplaced + 1).sh_offset);
Elf_Addr startAddr = rdi(shdrs.at(lastReplaced + 1).sh_addr);

debug("first reserved offset/addr is 0x%x/0x%llx\n",
startOffset, (unsigned long long) startAddr);

Expand Down Expand Up @@ -1238,7 +1240,7 @@ void ElfFile<ElfFileParamNames>::rewriteHeaders(Elf_Addr phdrAddress)
section. Note that not all executables have .dynamic sections
(e.g., those produced by klibc's klcc). */
auto shdrDynamic = tryFindSectionHeader(".dynamic");
if (shdrDynamic) {
if (shdrDynamic && rdi((*shdrDynamic).get().sh_type) != SHT_NOBITS) {
auto dyn_table = (Elf_Dyn *) (fileContents->data() + rdi((*shdrDynamic).get().sh_offset));
unsigned int d_tag;
for (auto dyn = dyn_table; (d_tag = rdi(dyn->d_tag)) != DT_NULL; dyn++)
Expand Down
3 changes: 2 additions & 1 deletion tests/Makefile.am
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Expand Up @@ -53,7 +53,8 @@ src_TESTS = \
shared-rpath.sh \
short-first-segment.sh \
empty-note.sh \
set-interpreter-same.sh
set-interpreter-same.sh \
debug-interp.sh

build_TESTS = \
$(no_rpath_arch_TESTS)
Expand Down
13 changes: 13 additions & 0 deletions tests/debug-interp.sh
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@@ -0,0 +1,13 @@
#! /bin/sh -e
SCRATCH=scratch/$(basename "$0" .sh)
OBJCOPY=${OBJCOPY:-objcopy}

rm -rf "${SCRATCH}"
mkdir -p "${SCRATCH}"

cp simple "${SCRATCH}/"

${OBJCOPY} --only-keep-debug "${SCRATCH}/simple" "${SCRATCH}/simple.debug"

# Check if patchelf handles debug-only executables
../src/patchelf --set-interpreter /oops "${SCRATCH}/simple.debug"