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tinycc/x86_64-link.c
Michael Matz 975c74c1f5 x86-64: Prefer 32S relocations 
This target has _32 and _32S relocs (the latter being for signed
32 bit entities).  All instruction displacements have to use
the 32S variants.  Normal references like
  .long s
normally would use the _32 variant.  For normal executables this
doesn't matter.  For shared libraries neither (which use PC-relative
relocs).  But it matters for things like the kernel that are linked
to high addresses (signed ones).  There the GNU linker would error
out on overflow for the _32 variant.

To keep life simple we simply switch from _32 to _32S altogether.
Strictly speaking it's still wrong, but in practice using _32 is
more often wrong than using _32S ;)
2016-12-15 17:47:12 +01:00

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#ifdef TARGET_DEFS_ONLY
#define EM_TCC_TARGET EM_X86_64
/* relocation type for 32 bit data relocation */
#define R_DATA_32 R_X86_64_32S
#define R_DATA_PTR R_X86_64_64
#define R_JMP_SLOT R_X86_64_JUMP_SLOT
#define R_GLOB_DAT R_X86_64_GLOB_DAT
#define R_COPY R_X86_64_COPY
#define R_NUM R_X86_64_NUM
#define ELF_START_ADDR 0x400000
#define ELF_PAGE_SIZE 0x200000
#define PCRELATIVE_DLLPLT 1
#define RELOCATE_DLLPLT 1
#else /* !TARGET_DEFS_ONLY */
#include "tcc.h"
/* Returns 1 for a code relocation, 0 for a data relocation. For unknown
relocations, returns -1. */
int code_reloc (int reloc_type)
{
switch (reloc_type) {
case R_X86_64_32:
case R_X86_64_32S:
case R_X86_64_64:
case R_X86_64_GOTPCREL:
case R_X86_64_GOTPCRELX:
case R_X86_64_REX_GOTPCRELX:
case R_X86_64_GOTTPOFF:
case R_X86_64_GOT32:
case R_X86_64_GLOB_DAT:
case R_X86_64_COPY:
case R_X86_64_RELATIVE:
return 0;
case R_X86_64_PC32:
case R_X86_64_PLT32:
case R_X86_64_JUMP_SLOT:
return 1;
}
tcc_error ("Unknown relocation type: %d", reloc_type);
return -1;
}
/* Returns an enumerator to describe wether and when the relocation needs a
GOT and/or PLT entry to be created. See tcc.h for a description of the
different values. */
int gotplt_entry_type (int reloc_type)
{
switch (reloc_type) {
case R_X86_64_GLOB_DAT:
case R_X86_64_JUMP_SLOT:
case R_X86_64_COPY:
case R_X86_64_RELATIVE:
return NO_GOTPLT_ENTRY;
case R_X86_64_32:
case R_X86_64_32S:
case R_X86_64_64:
case R_X86_64_PC32:
return AUTO_GOTPLT_ENTRY;
case R_X86_64_GOTTPOFF:
return BUILD_GOT_ONLY;
case R_X86_64_GOT32:
case R_X86_64_GOTPCREL:
case R_X86_64_GOTPCRELX:
case R_X86_64_REX_GOTPCRELX:
case R_X86_64_PLT32:
return ALWAYS_GOTPLT_ENTRY;
}
tcc_error ("Unknown relocation type: %d", reloc_type);
return -1;
}
ST_FUNC unsigned create_plt_entry(TCCState *s1, unsigned got_offset, struct sym_attr *attr)
{
Section *plt = s1->plt;
uint8_t *p;
int modrm;
unsigned plt_offset, relofs;
modrm = 0x25;
/* empty PLT: create PLT0 entry that pushes the library indentifier
(GOT + PTR_SIZE) and jumps to ld.so resolution routine
(GOT + 2 * PTR_SIZE) */
if (plt->data_offset == 0) {
p = section_ptr_add(plt, 16);
p[0] = 0xff; /* pushl got + PTR_SIZE */
p[1] = modrm + 0x10;
write32le(p + 2, PTR_SIZE);
p[6] = 0xff; /* jmp *(got + PTR_SIZE * 2) */
p[7] = modrm;
write32le(p + 8, PTR_SIZE * 2);
}
plt_offset = plt->data_offset;
/* The PLT slot refers to the relocation entry it needs via offset.
The reloc entry is created below, so its offset is the current
data_offset */
relofs = s1->got->reloc ? s1->got->reloc->data_offset : 0;
/* Jump to GOT entry where ld.so initially put the address of ip + 4 */
p = section_ptr_add(plt, 16);
p[0] = 0xff; /* jmp *(got + x) */
p[1] = modrm;
write32le(p + 2, got_offset);
p[6] = 0x68; /* push $xxx */
/* On x86-64, the relocation is referred to by _index_ */
write32le(p + 7, relofs / sizeof (ElfW_Rel));
p[11] = 0xe9; /* jmp plt_start */
write32le(p + 12, -(plt->data_offset));
return plt_offset;
}
/* relocate the PLT: compute addresses and offsets in the PLT now that final
address for PLT and GOT are known (see fill_program_header) */
ST_FUNC void relocate_plt(TCCState *s1)
{
uint8_t *p, *p_end;
if (!s1->plt)
return;
p = s1->plt->data;
p_end = p + s1->plt->data_offset;
if (p < p_end) {
int x = s1->got->sh_addr - s1->plt->sh_addr - 6;
add32le(p + 2, x);
add32le(p + 8, x - 6);
p += 16;
while (p < p_end) {
add32le(p + 2, x + s1->plt->data - p);
p += 16;
}
}
}
static ElfW_Rel *qrel; /* ptr to next reloc entry reused */
void relocate_init(Section *sr)
{
qrel = (ElfW_Rel *) sr->data;
}
void relocate(TCCState *s1, ElfW_Rel *rel, int type, char *ptr, addr_t addr, addr_t val)
{
int sym_index, esym_index;
sym_index = ELFW(R_SYM)(rel->r_info);
switch (type) {
case R_X86_64_64:
if (s1->output_type == TCC_OUTPUT_DLL) {
esym_index = s1->sym_attrs[sym_index].dyn_index;
qrel->r_offset = rel->r_offset;
if (esym_index) {
qrel->r_info = ELFW(R_INFO)(esym_index, R_X86_64_64);
qrel->r_addend = rel->r_addend;
qrel++;
break;
} else {
qrel->r_info = ELFW(R_INFO)(0, R_X86_64_RELATIVE);
qrel->r_addend = read64le(ptr) + val;
qrel++;
}
}
add64le(ptr, val);
break;
case R_X86_64_32:
case R_X86_64_32S:
if (s1->output_type == TCC_OUTPUT_DLL) {
/* XXX: this logic may depend on TCC's codegen
now TCC uses R_X86_64_32 even for a 64bit pointer */
qrel->r_info = ELFW(R_INFO)(0, R_X86_64_RELATIVE);
/* Use sign extension! */
qrel->r_addend = (int)read32le(ptr) + val;
qrel++;
}
add32le(ptr, val);
break;
case R_X86_64_PC32:
if (s1->output_type == TCC_OUTPUT_DLL) {
/* DLL relocation */
esym_index = s1->sym_attrs[sym_index].dyn_index;
if (esym_index) {
qrel->r_offset = rel->r_offset;
qrel->r_info = ELFW(R_INFO)(esym_index, R_X86_64_PC32);
/* Use sign extension! */
qrel->r_addend = (int)read32le(ptr) + rel->r_addend;
qrel++;
break;
}
}
goto plt32pc32;
case R_X86_64_PLT32:
/* fallthrough: val already holds the PLT slot address */
plt32pc32:
{
long long diff;
diff = (long long)val - addr;
if (diff < -2147483648LL || diff > 2147483647LL) {
tcc_error("internal error: relocation failed");
}
add32le(ptr, diff);
}
break;
case R_X86_64_GLOB_DAT:
case R_X86_64_JUMP_SLOT:
/* They don't need addend */
write64le(ptr, val - rel->r_addend);
break;
case R_X86_64_GOTPCREL:
case R_X86_64_GOTPCRELX:
case R_X86_64_REX_GOTPCRELX:
add32le(ptr, s1->got->sh_addr - addr +
s1->sym_attrs[sym_index].got_offset - 4);
break;
case R_X86_64_GOTTPOFF:
add32le(ptr, val - s1->got->sh_addr);
break;
case R_X86_64_GOT32:
/* we load the got offset */
add32le(ptr, s1->sym_attrs[sym_index].got_offset);
break;
case R_X86_64_RELATIVE:
/* do nothing */
break;
}
}
#endif /* !TARGET_DEFS_ONLY */
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