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PackLinuxElf32::canPackOSABI() isolates canPack() from OSABI weirdness

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modified:   p_lx_elf.cpp
	modified:   p_lx_elf.h
This commit is contained in:
John Reiser
2023-03-16 08:30:06 -07:00
parent b74c4e4ac1
commit 1320e3efdb
2 changed files with 62 additions and 52 deletions
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113
src/p_lx_elf.cpp
View File

@ -2337,56 +2337,10 @@ int PackLinuxElf32::canUnpack() // bool, except -1: format known, but not packed
return false;
}
bool PackLinuxElf32::canPack()
bool // false [often throwCantPack]: some defect; true: good so far
PackLinuxElf32::canPackOSABI(Elf32_Ehdr const *ehdr)
{
union {
unsigned char buf[MAX_ELF_HDR_32];
//struct { Elf32_Ehdr ehdr; Elf32_Phdr phdr; } e;
} u;
COMPILE_TIME_ASSERT(sizeof(u.buf) <= (2*512))
// Design with "extra" Shdrs in output at xct_off DOES NOT WORK
// because code for EM_ARM has embedded relocations
// that are not made visible, such as:
// ----- glibc-2.31/sysdeps/arm/crti.S
// .type call_weak_fn, %function
// call_weak_fn:
// ldr r3, .LGOT
// ldr r2, .LGOT+4
// .LPIC:
// add r3, pc, r3
// ldr r2, [r3, r2]
// cmp r2, #0
// bxeq lr
// b PREINIT_FUNCTION
// .p2align 2
// .LGOT:
// .word _GLOBAL_OFFSET_TABLE_-(.LPIC+8) // unseen reloc!
// .word PREINIT_FUNCTION(GOT)
// -----
// So, PackUnix::PackUnix() disables (but silently accepts) --android-shlib,
// and see if appending ARM_ATTRIBUTES Shdr is good enough.
fi->seek(0, SEEK_SET);
fi->readx(u.buf, sizeof(u.buf));
fi->seek(0, SEEK_SET);
Elf32_Ehdr const *const ehdr = (Elf32_Ehdr *) u.buf;
// now check the ELF header
if (checkEhdr(ehdr) != 0)
return false;
// additional requirements for linux/elf386
if (get_te16(&ehdr->e_ehsize) != sizeof(*ehdr)) {
throwCantPack("invalid Ehdr e_ehsize; try '--force-execve'");
return false;
}
if (e_phoff != sizeof(*ehdr)) {// Phdrs not contiguous with Ehdr
throwCantPack("non-contiguous Ehdr/Phdr; try '--force-execve'");
return false;
}
unsigned char osabi0 = u.buf[Elf32_Ehdr::EI_OSABI];
unsigned char osabi0 = ehdr->e_ident[Elf32_Ehdr::EI_OSABI];
// The first PT_LOAD32 must cover the beginning of the file (0==p_offset).
Elf32_Phdr const *phdr = phdri;
note_size = 0;
@ -2461,9 +2415,63 @@ bool PackLinuxElf32::canPack()
if (osabi0!=ei_osabi) {
return false;
}
return true; // good so far
}
bool PackLinuxElf32::canPack()
{
union {
unsigned char buf[MAX_ELF_HDR_32];
//struct { Elf32_Ehdr ehdr; Elf32_Phdr phdr; } e;
} u;
COMPILE_TIME_ASSERT(sizeof(u.buf) <= (2*512))
// My earlier design with "extra" Shdrs in output at xct_off
// DOES NOT WORK because code for EM_ARM has embedded relocations
// that are not made visible, such as:
// ----- glibc-2.31/sysdeps/arm/crti.S
// .type call_weak_fn, %function
// call_weak_fn:
// ldr r3, .LGOT
// ldr r2, .LGOT+4
// .LPIC:
// add r3, pc, r3
// ldr r2, [r3, r2]
// cmp r2, #0
// bxeq lr
// b PREINIT_FUNCTION
// .p2align 2
// .LGOT:
// .word _GLOBAL_OFFSET_TABLE_-(.LPIC+8) // unseen reloc!
// .word PREINIT_FUNCTION(GOT)
// -----
// So, PackUnix::PackUnix() disables (but silently accepts) --android-shlib,
// and see if appending ARM_ATTRIBUTES Shdr is good enough.
fi->seek(0, SEEK_SET);
fi->readx(u.buf, sizeof(u.buf));
fi->seek(0, SEEK_SET);
Elf32_Ehdr const *const ehdr = (Elf32_Ehdr *) u.buf;
// now check the ELF header
if (checkEhdr(ehdr) != 0)
return false;
// additional requirements for linux/elf386
if (get_te16(&ehdr->e_ehsize) != sizeof(*ehdr)) {
throwCantPack("invalid Ehdr e_ehsize; try '--force-execve'");
return false;
}
if (e_phoff != sizeof(*ehdr)) {// Phdrs not contiguous with Ehdr
throwCantPack("non-contiguous Ehdr/Phdr; try '--force-execve'");
return false;
}
if (!canPackOSABI((Elf32_Ehdr *)u.buf)) {
return false;
}
upx_uint32_t max_LOADsz = 0, max_offset = 0;
phdr = phdri;
Elf32_Phdr *phdr = phdri;
for (unsigned j=0; j < e_phnum; ++phdr, ++j) {
if (j > ((MAX_ELF_HDR_32 - sizeof(Elf32_Ehdr)) / sizeof(Elf32_Phdr))) {
throwCantPack("too many ElfXX_Phdr; try '--force-execve'");
@ -2795,8 +2803,9 @@ bool PackLinuxElf32::canPack()
}
goto proceed; // But proper packing depends on checking xct_va.
}
else
else {
throwCantPack("need DT_INIT; try \"void _init(void){}\"");
}
abandon:
return false;
proceed: ;
@ -3004,7 +3013,7 @@ PackLinuxElf64::canPack()
// into good positions when building the original shared library,
// and also requires ld-linux to behave.
if (elf_find_dynamic(upx_dt_init)) {
if (/*jni_onload_sym ||*/ elf_find_dynamic(upx_dt_init)) {
if (elf_has_dynamic(Elf64_Dyn::DT_TEXTREL)) {
throwCantPack("DT_TEXTREL found; re-compile with -fPIC");
goto abandon;

1
src/p_lx_elf.h
View File

@ -138,6 +138,7 @@ public:
protected:
virtual void PackLinuxElf32help1(InputFile *f);
virtual int checkEhdr(Elf32_Ehdr const *ehdr) const;
virtual bool canPackOSABI(Elf32_Ehdr const *);
virtual bool canPack() override;
virtual int canUnpack() override; // bool, except -1: format known, but not packed