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/* --------------------------------------------------------------------------
* Symbol Extras.
* This is about allocating a small chunk of memory for every symbol in the
* object file. We make sure that the SymboLExtras are always "in range" of
* limited-range PC-relative instructions on various platforms by allocating
* them right next to the object code itself.
*
* This implementation is shared by the MachO and ELF implementations. Windows'
* PEi386 has its own implementation of symbol extras.
*/
#include "LinkerInternals.h"
#if defined(NEED_SYMBOL_EXTRAS)
#if !defined(x86_64_HOST_ARCH) || !defined(mingw32_HOST_OS)
#include "RtsUtils.h"
#include "sm/OSMem.h"
#include "linker/SymbolExtras.h"
#include "linker/M32Alloc.h"
#if defined(OBJFORMAT_ELF)
# include "linker/Elf.h"
#elif defined(OBJFORMAT_MACHO)
# include "linker/MachO.h"
#endif
#include <string.h>
#if RTS_LINKER_USE_MMAP
#include <sys/mman.h>
#endif /* RTS_LINKER_USE_MMAP */
/*
ocAllocateExtras
Allocate additional space at the end of the object file image to make room
for jump islands (powerpc, x86_64, arm), GOT entries (x86_64) and
bss sections.
PowerPC relative branch instructions have a 24 bit displacement field.
As PPC code is always 4-byte-aligned, this yields a +-32MB range.
If a particular imported symbol is outside this range, we have to redirect
the jump to a short piece of new code that just loads the 32bit absolute
address and jumps there.
On x86_64, PC-relative jumps and PC-relative accesses to the GOT are limited
to 32 bits (+-2GB).
This function just allocates space for one SymbolExtra for every
undefined symbol in the object file. The code for the jump islands is
filled in by makeSymbolExtra below.
*/
int ocAllocateExtras(ObjectCode* oc, int count, int first, int bssSize)
{
void* oldImage = oc->image;
const size_t extras_size = sizeof(SymbolExtra) * count;
if (count > 0 || bssSize > 0) {
if (!RTS_LINKER_USE_MMAP) {
/* N.B. We currently can't mark symbol extras as non-executable in this
* case. */
// round up to the nearest 4
int aligned = (oc->fileSize + 3) & ~3;
int misalignment = oc->misalignment;
oc->image -= misalignment;
oc->image = stgReallocBytes( oc->image,
misalignment +
aligned + extras_size,
"ocAllocateExtras" );
oc->image += misalignment;
oc->symbol_extras = (SymbolExtra *) (oc->image + aligned);
} else if (USE_CONTIGUOUS_MMAP || RtsFlags.MiscFlags.linkerAlwaysPic) {
/* Keep image, bssExtras and symbol_extras contiguous */
/* N.B. We currently can't mark symbol extras as non-executable in this
* case. */
size_t n = roundUpToPage(oc->fileSize);
// round bssSize up to the nearest page size since we need to ensure that
// symbol_extras is aligned to a page boundary so it can be mprotect'd.
bssSize = roundUpToPage(bssSize);
size_t allocated_size = n + bssSize + extras_size;
void *new = mmapAnonForLinker(allocated_size);
if (new) {
memcpy(new, oc->image, oc->fileSize);
if (oc->imageMapped) {
munmapForLinker(oc->image, n, "ocAllocateExtras");
}
oc->image = new;
oc->imageMapped = true;
oc->fileSize = allocated_size;
oc->symbol_extras = (SymbolExtra *) (oc->image + n + bssSize);
oc->bssBegin = oc->image + n;
oc->bssEnd = oc->image + n + bssSize;
}
else {
oc->symbol_extras = NULL;
return 0;
}
} else {
/* m32_allocator_flush ensures that these are marked as executable when
* we finish building them. */
oc->symbol_extras = m32_alloc(oc->rx_m32, extras_size, 8);
if (oc->symbol_extras == NULL) return 0;
}
}
if (oc->symbol_extras != NULL) {
memset( oc->symbol_extras, 0, extras_size );
}
// ObjectCodeFormatInfo contains computed addresses based on offset to
// image, if the address of image changes, we need to invalidate
// the ObjectCodeFormatInfo and recompute it.
if (oc->image != oldImage) {
#if defined(OBJFORMAT_MACHO)
ocInit_MachO( oc );
#endif
#if defined(OBJFORMAT_ELF)
ocInit_ELF( oc );
#endif
}
oc->first_symbol_extra = first;
oc->n_symbol_extras = count;
return 1;
}
/**
* Mark the symbol extras as non-writable.
*/
void ocProtectExtras(ObjectCode* oc)
{
if (oc->n_symbol_extras == 0) return;
if (!RTS_LINKER_USE_MMAP) {
/*
* In this case the symbol extras were allocated via malloc. All we can do
* in this case is hope that the platform doesn't mark such allocations as
* non-executable.
*/
} else if (USE_CONTIGUOUS_MMAP || RtsFlags.MiscFlags.linkerAlwaysPic) {
mmapForLinkerMarkExecutable(oc->symbol_extras, sizeof(SymbolExtra) * oc->n_symbol_extras);
} else {
/*
* The symbol extras were allocated via m32. They will be protected when
* the m32 allocator is finalized
*/
}
}
#if defined(powerpc_HOST_ARCH) || defined(x86_64_HOST_ARCH)
SymbolExtra* makeSymbolExtra( ObjectCode const* oc,
unsigned long symbolNumber,
unsigned long target )
{
SymbolExtra *extra;
ASSERT( symbolNumber >= oc->first_symbol_extra
&& symbolNumber - oc->first_symbol_extra < oc->n_symbol_extras);
extra = &oc->symbol_extras[symbolNumber - oc->first_symbol_extra];
#if defined(powerpc_HOST_ARCH)
// lis r12, hi16(target)
extra->jumpIsland.lis_r12 = 0x3d80;
extra->jumpIsland.hi_addr = target >> 16;
// ori r12, r12, lo16(target)
extra->jumpIsland.ori_r12_r12 = 0x618c;
extra->jumpIsland.lo_addr = target & 0xffff;
// mtctr r12
extra->jumpIsland.mtctr_r12 = 0x7d8903a6;
// bctr
extra->jumpIsland.bctr = 0x4e800420;
#endif /* powerpc_HOST_ARCH */
#if defined(x86_64_HOST_ARCH)
// jmp *-14(%rip)
// 0xFF 25 is opcode + ModRM of near absolute indirect jump
// Two bytes trailing padding, needed for TLSGD GOT entries
// See Note [TLSGD relocation] in elf_tlsgd.c
static uint8_t jmp[] = { 0xFF, 0x25, 0xF2, 0xFF, 0xFF, 0xFF, 0x00, 0x00 };
extra->addr = target;
memcpy(extra->jumpIsland, jmp, 8);
#endif /* x86_64_HOST_ARCH */
return extra;
}
#endif /* powerpc_HOST_ARCH || x86_64_HOST_ARCH */
#endif /* !x86_64_HOST_ARCH) || !mingw32_HOST_OS */
#endif // NEED_SYMBOL_EXTRAS
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