From 2fc88e736892981b8b2b46661ac11f14dc351bc8 Mon Sep 17 00:00:00 2001 From: Simon Marlow Date: Thu, 18 Oct 2007 12:52:20 +0000 Subject: [PATCH] add PIC relocations for x86_64, and use a simpler hack in place of x86_64_high_symbol() This is Wolfgang Thaller's patch sent to cvs-ghc recently, with extra commentary by me. It turns out that this patch is not just a cleanup, it is also necessary for GHCi to work on x86_64 with shared libraries, because previously lookupSymbol() was creating jump-table entries for all symbols looked up that resolved outside 2Gb, whereas Wolfgang's version only generates jump-table entries for 32-bit symbol references in object code that we load. --- rts/Linker.c | 168 +++++++++++++++++++++++++++------------------------------- 1 file changed, 79 insertions(+), 89 deletions(-) diff --git a/rts/Linker.c b/rts/Linker.c index 65a7e22..81709f7 100644 --- a/rts/Linker.c +++ b/rts/Linker.c @@ -107,7 +107,7 @@ ObjectCode *objects = NULL; /* initially empty */ static int ocVerifyImage_ELF ( ObjectCode* oc ); static int ocGetNames_ELF ( ObjectCode* oc ); static int ocResolve_ELF ( ObjectCode* oc ); -#if defined(powerpc_HOST_ARCH) +#if defined(powerpc_HOST_ARCH) || defined(x86_64_HOST_ARCH) static int ocAllocateSymbolExtras_ELF ( ObjectCode* oc ); #endif #elif defined(OBJFORMAT_PEi386) @@ -128,9 +128,30 @@ static void machoInitSymbolsWithoutUnderscore( void ); #endif #endif -#if defined(x86_64_HOST_ARCH) && defined(OBJFORMAT_ELF) -static void*x86_64_high_symbol( char *lbl, void *addr ); -#endif +/* on x86_64 we have a problem with relocating symbol references in + * code that was compiled without -fPIC. By default, the small memory + * model is used, which assumes that symbol references can fit in a + * 32-bit slot. The system dynamic linker makes this work for + * references to shared libraries by either (a) allocating a jump + * table slot for code references, or (b) moving the symbol at load + * time (and copying its contents, if necessary) for data references. + * + * We unfortunately can't tell whether symbol references are to code + * or data. So for now we assume they are code (the vast majority + * are), and allocate jump-table slots. Unfortunately this will + * SILENTLY generate crashing code for data references. This hack is + * enabled by X86_64_ELF_NONPIC_HACK. + * + * One workaround is to use shared Haskell libraries. This is + * coming. Another workaround is to keep the static libraries but + * compile them with -fPIC, because that will generate PIC references + * to data which can be relocated. The PIC code is still too green to + * do this systematically, though. + * + * See bug #781 + * See thread http://www.haskell.org/pipermail/cvs-ghc/2007-September/038458.html + */ +#define X86_64_ELF_NONPIC_HACK 1 /* ----------------------------------------------------------------------------- * Built-in symbols from the RTS @@ -1059,19 +1080,7 @@ lookupSymbol( char *lbl ) if (val == NULL) { # if defined(OBJFORMAT_ELF) -# if defined(x86_64_HOST_ARCH) - val = dlsym(dl_prog_handle, lbl); - if (val >= (void *)0x80000000) { - void *new_val; - new_val = x86_64_high_symbol(lbl, val); - IF_DEBUG(linker,debugBelch("lookupSymbol: relocating out of range symbol: %s = %p, now %p\n", lbl, val, new_val)); - return new_val; - } else { - return val; - } -# else return dlsym(dl_prog_handle, lbl); -# endif # elif defined(OBJFORMAT_MACHO) # if HAVE_DLFCN_H /* On OS X 10.3 and later, we use dlsym instead of the old legacy @@ -1350,7 +1359,7 @@ loadObj( char *path ) # if defined(OBJFORMAT_MACHO) && (defined(powerpc_HOST_ARCH) || defined(x86_64_HOST_ARCH)) r = ocAllocateSymbolExtras_MachO ( oc ); if (!r) { return r; } -# elif defined(OBJFORMAT_ELF) && defined(powerpc_HOST_ARCH) +# elif defined(OBJFORMAT_ELF) && (defined(powerpc_HOST_ARCH) || defined(x86_64_HOST_ARCH)) r = ocAllocateSymbolExtras_ELF ( oc ); if (!r) { return r; } #endif @@ -1532,8 +1541,7 @@ static void addSection ( ObjectCode* oc, SectionKind kind, * them right next to the object code itself. */ -#if defined(powerpc_HOST_ARCH) || (defined(x86_64_HOST_ARCH) \ - && defined(darwin_TARGET_OS)) +#if defined(powerpc_HOST_ARCH) || defined(x86_64_HOST_ARCH) /* ocAllocateSymbolExtras @@ -1560,10 +1568,12 @@ static int ocAllocateSymbolExtras( ObjectCode* oc, int count, int first ) int pagesize, n, m; #endif int aligned; +#ifndef USE_MMAP int misalignment = 0; -#if darwin_HOST_OS +#ifdef darwin_HOST_OS misalignment = oc->misalignment; #endif +#endif if( count > 0 ) { @@ -2744,64 +2754,6 @@ PLTSize(void) #endif -#if x86_64_HOST_ARCH -// On x86_64, 32-bit relocations are often used, which requires that -// we can resolve a symbol to a 32-bit offset. However, shared -// libraries are placed outside the 2Gb area, which leaves us with a -// problem when we need to give a 32-bit offset to a symbol in a -// shared library. -// -// For a function symbol, we can allocate a bounce sequence inside the -// 2Gb area and resolve the symbol to this. The bounce sequence is -// simply a long jump instruction to the real location of the symbol. -// -// For data references, we're screwed. -// -typedef struct { - unsigned char jmp[8]; /* 6 byte instruction: jmpq *0x00000002(%rip) */ - void *addr; -} x86_64_bounce; - -#define X86_64_BB_SIZE 1024 - -static x86_64_bounce *x86_64_bounce_buffer = NULL; -static nat x86_64_bb_next_off; - -static void* -x86_64_high_symbol( char *lbl, void *addr ) -{ - x86_64_bounce *bounce; - - if ( x86_64_bounce_buffer == NULL || - x86_64_bb_next_off >= X86_64_BB_SIZE ) { - x86_64_bounce_buffer = - mmap(NULL, X86_64_BB_SIZE * sizeof(x86_64_bounce), - PROT_EXEC|PROT_READ|PROT_WRITE, - MAP_PRIVATE|EXTRA_MAP_FLAGS|MAP_ANONYMOUS, -1, 0); - if (x86_64_bounce_buffer == MAP_FAILED) { - barf("x86_64_high_symbol: mmap failed"); - } - x86_64_bb_next_off = 0; - } - bounce = &x86_64_bounce_buffer[x86_64_bb_next_off]; - bounce->jmp[0] = 0xff; - bounce->jmp[1] = 0x25; - bounce->jmp[2] = 0x02; - bounce->jmp[3] = 0x00; - bounce->jmp[4] = 0x00; - bounce->jmp[5] = 0x00; - bounce->addr = addr; - x86_64_bb_next_off++; - - IF_DEBUG(linker, debugBelch("x86_64: allocated bounce entry for %s->%p at %p\n", - lbl, addr, bounce)); - - insertStrHashTable(symhash, lbl, bounce); - return bounce; -} -#endif - - /* * Generic ELF functions */ @@ -3517,9 +3469,15 @@ do_Elf_Rela_relocations ( ObjectCode* oc, char* ehdrC, { StgInt64 off = value - P; if (off >= 0x7fffffffL || off < -0x80000000L) { - barf("R_X86_64_PC32 relocation out of range: %s = %p", - symbol, off); - } +#if X86_64_ELF_NONPIC_HACK + StgInt64 pltAddress = (StgInt64) &makeSymbolExtra(oc, ELF_R_SYM(info), S) + -> jumpIsland; + off = pltAddress + A - P; +#else + barf("R_X86_64_PC32 relocation out of range: %s = %p\nRecompile %s with -fPIC.", + symbol, off, oc->fileName ); +#endif + } *(Elf64_Word *)P = (Elf64_Word)off; break; } @@ -3533,19 +3491,51 @@ do_Elf_Rela_relocations ( ObjectCode* oc, char* ehdrC, case R_X86_64_32: if (value >= 0x7fffffffL) { - barf("R_X86_64_32 relocation out of range: %s = %p\n", - symbol, value); - } +#if X86_64_ELF_NONPIC_HACK + StgInt64 pltAddress = (StgInt64) &makeSymbolExtra(oc, ELF_R_SYM(info), S) + -> jumpIsland; + value = pltAddress + A; +#else + barf("R_X86_64_32 relocation out of range: %s = %p\nRecompile %s with -fPIC.", + symbol, value, oc->fileName ); +#endif + } *(Elf64_Word *)P = (Elf64_Word)value; break; case R_X86_64_32S: if ((StgInt64)value > 0x7fffffffL || (StgInt64)value < -0x80000000L) { - barf("R_X86_64_32S relocation out of range: %s = %p\n", - symbol, value); +#if X86_64_ELF_NONPIC_HACK + StgInt64 pltAddress = (StgInt64) &makeSymbolExtra(oc, ELF_R_SYM(info), S) + -> jumpIsland; + value = pltAddress + A; +#else + barf("R_X86_64_32S relocation out of range: %s = %p\nRecompile %s with -fPIC.", + symbol, value, oc->fileName ); +#endif } *(Elf64_Sword *)P = (Elf64_Sword)value; break; + + case R_X86_64_GOTPCREL: + { + StgInt64 gotAddress = (StgInt64) &makeSymbolExtra(oc, ELF_R_SYM(info), S)->addr; + StgInt64 off = gotAddress + A - P; + *(Elf64_Word *)P = (Elf64_Word)off; + break; + } + + case R_X86_64_PLT32: + { + StgInt64 off = value - P; + if (off >= 0x7fffffffL || off < -0x80000000L) { + StgInt64 pltAddress = (StgInt64) &makeSymbolExtra(oc, ELF_R_SYM(info), S) + -> jumpIsland; + off = pltAddress + A - P; + } + *(Elf64_Word *)P = (Elf64_Word)off; + break; + } #endif default: @@ -3698,10 +3688,10 @@ ia64_reloc_pcrel21(Elf_Addr target, Elf_Addr value, ObjectCode *oc) #endif /* ia64 */ /* - * PowerPC ELF specifics + * PowerPC & X86_64 ELF specifics */ -#ifdef powerpc_HOST_ARCH +#if defined(powerpc_HOST_ARCH) || defined(x86_64_HOST_ARCH) static int ocAllocateSymbolExtras_ELF( ObjectCode *oc ) { @@ -3725,7 +3715,7 @@ static int ocAllocateSymbolExtras_ELF( ObjectCode *oc ) if( shdr[i].sh_entsize != sizeof( Elf_Sym ) ) { errorBelch( "The entry size (%d) of the symtab isn't %d\n", - shdr[i].sh_entsize, sizeof( Elf_Sym ) ); + (int) shdr[i].sh_entsize, (int) sizeof( Elf_Sym ) ); return 0; } -- 1.7.10.4