--- uClibc-0.9.27/ldso/include/dl-elf.h 2005-01-11 23:59:21.000000000 -0800 +++ uClibc-0.9.27/ldso/include/dl-elf.h 2005-08-12 18:24:43.000000000 -0700 @@ -112,6 +112,13 @@ # define ELF_RTYPE_CLASS_COPY (0x2) #endif #define ELF_RTYPE_CLASS_PLT (0x1) +/* The type class can be qualified by a list (mask) of the acceptable + * STT_ symbol types, if not given the default is everything numerically + * <= STT_FUNC (from the original code...) + */ +#define ELF_RTYPE_CLASS_OF(type) ((1<<2) << (type)) +#define ELF_RTYPE_CLASS_ALL (0xffff << 2) +#define ELF_RTYPE_CLASS_DEFAULT (((ELF_RTYPE_CLASS_OF(STT_FUNC) << 1) - 1)&ELF_RTYPE_CLASS_ALL) /* Convert between the Linux flags for page protections and the --- uClibc-0.9.27/ldso/ldso/arm/resolve.S 2005-01-11 23:59:21.000000000 -0800 +++ uClibc-0.9.27/ldso/ldso/arm/resolve.S 2005-08-13 15:08:27.523344709 -0700 @@ -1,43 +1,117 @@ /* - * This function is _not_ called directly. It is jumped to (so no return - * address is on the stack) when attempting to use a symbol that has not yet - * been resolved. The first time a jump symbol (such as a function call inside - * a shared library) is used (before it gets resolved) it will jump here to - * _dl_linux_resolve. When we get called the stack looks like this: - * reloc_entry - * tpnt - * - * This function saves all the registers, puts a copy of reloc_entry and tpnt - * on the stack (as function arguments) then make the function call - * _dl_linux_resolver(tpnt, reloc_entry). _dl_linux_resolver() figures out - * where the jump symbol is _really_ supposed to have jumped to and returns - * that to us. Once we have that, we overwrite tpnt with this fixed up - * address. We then clean up after ourselves, put all the registers back how we - * found them, then we jump to the fixed up address, which is where the jump - * symbol that got us here really wanted to jump to in the first place. - * -Erik Andersen + * On ARM the PLT contains the following three instructions (for ARM calls): + * + * add ip, pc, #0xNN00000 + * add ip, ip, #0xNN000 + * ldr pc, [ip, #0xNNN]! + * + * So that, effectively, causes the following to happen: + * + * ip := pc+0x0NNNNNNN + * pc := *ip + * + * For thumb the above fragment is preceded by "bx pc, nop" to switch to ARM + * mode and the thumb 'bl' must go to PLT-4 - the PLT entry is expanded by + * four bytes to accomodate the trampoline code. + * + * 0x0NNNNNNN is the offset of the GOT entry for this function relative to + * the PLT entry for this function (where the code is). So the code in the + * PLT causes a branch to whatever is in the GOT, leaving the actual address + * of the GOT entry in ip. (Note that the GOT must follow the PLT - the + * added value is 28 bit unsigned). + * + * ip is a pointer to the GOT entry for this function, the first time round + * *ip points to this code: + * + * str lr, [sp, #-4]! @ save lr + * ldr lr, [pc, #4] @ lr := *dat (&GOT_TABLE[0]-.) + * add lr, pc, lr @ lr += &dat (so lr == &GOT_TABLE[0]) + * ldr pc, [lr, #8]! @ pc := GOT_TABLE[2] + *dat: .long &GOT_TABLE[0] - . + * + * (this code is actually held in the first entry of the PLT). The code + * preserves lr then uses it as a scratch register (this preserves the ip + * value calculated above). GOT_TABLE[2] is initialized by INIT_GOT in + * dl-sysdep.h to point to _dl_linux_resolve - this function. The first + * three entries in the GOT are reserved, then they are followed by the + * entries for the PLT entries, in order. + * + * The linker initialises the following (non-reserved) GOT entries to + * the offset of the PLT with an associated relocation so that on load + * the entry is relocated to point to the PLT - the above code. + * + * The net effect of all this is that on the first call to an external (as + * yet unresolved) function all seven of the above instructions are + * executed in sequence and the program ends up executing _dl_linux_resolve + * with the following important values in registers: + * + * ip - a pointer to the GOT entry for the as yet unresolved function + * lr - &GOT_TABLE[2] + * + * GOT_TABLE[2] has already been initialised to _dl_linux_resolve, and + * GOT_TABLE[1] is a pointer to the (elf_resolve*) from INIT_GOT. + * _dl_linux_resolve unfrobnicates the ip and lr values to obtain arguments + * for a call to _dl_linux_resolver (not the additional 'r' on the end) - + * this is in elfinterp.c in this directory. The call takes arguments: + * + * _dl_linux_resolver(struct elf_resolve *tpnt, int reloc_entry) + * + * And returns the address of the function, it also overwrites the GOT + * table entry so that the next time round only the first code fragment will + * be executed - it will call the function directly. + * + * [[Of course, this simply doesn't work on ARM 4T with a thumb target - because + * 4T did not do the thumb/arm change on ldr pc! It can be made to work by + * changing _dl_linux_resolver to return __%s_from_arm for an STT_TFUNC, but + * this hasn't been done, and there is no guarantee that the linker generated + * that glue anyway.]] + * + * _dl_linux_resolve gets the arguments to call the resolver as follows: + * + * tpnt GOT_TABLE[1], [lr-4] + * reloc-entry &GOT-&GOT_TABLE[3], (ip - lr - 4)/4 + * + * (I.e. 'GOT' means the table entry for this function, the thing for which + * ip holds the address.) The reloc-entry is passed as an index, since + * since the GOT table has 4 byte entries the code needs to divide this by 4 + * to get the actual index. + * + * John Bowler, August 13, 2005 - determined by experiment and examination + * of generated ARM code (there was no documentation...) + * + * This code is all ARM code - not thumb - _dl_linux_resolver may, itself, + * be thumb, in which case the linker will insert the appropriate glue. A + * call from thumb to the PLT hits the trampoline code described above. + * This code (now) builds a proper stack frame. + * + * The code does *not* set sb (r9,v6) - to do that the basic PLT instructions + * would need to save sb and load the new value and that would require + * support in the linker since it generates those instructions. (Also note + * that linux/uclibc seems to be using r10 - sl - as a PIC base register - see + * dl-startup.c). */ -#define sl r10 -#define fp r11 -#define ip r12 - .text .globl _dl_linux_resolve .type _dl_linux_resolve,%function .align 4; _dl_linux_resolve: - stmdb sp!, {r0, r1, r2, r3, sl, fp} - sub r1, ip, lr - sub r1, r1, #4 - add r1, r1, r1 - ldr r0, [lr, #-4] - mov r3,r0 + @ _dl_linux_resolver is a standard subroutine call, therefore it + @ preserves everything except r0-r3 (a1-a4), ip and lr. This + @ function must branch to the real function, and that expects + @ r0-r3 and lr to be as they were before the whole PLT stuff - + @ ip can be trashed. + stmdb sp!, {r0-r3} + ldr r0, [lr, #-4] @ r0 := [lr-4] (GOT_TABLE[1]) + sub r1, lr, ip @ r1 := (lr-ip) (a multple of 4) + mvn r1, r1, ASR #2 @ r1 := ~((lr-ip)>>2), since -x = (1+~x) + @ ~x = -x-1, therefore ~(r1>>2) = (-((lr-ip)>>2)-1) + @ = - ((lr-ip)/4) - 1 = (ip - lr - 4)/4, as required bl _dl_linux_resolver - mov ip, r0 - ldmia sp!, {r0, r1, r2, r3, sl, fp, lr} - mov pc,ip + mov ip, r0 + ldmia sp!, {r0-r3, lr} + bx ip .size _dl_linux_resolve, .-_dl_linux_resolve --- uClibc-0.9.27/ldso/ldso/arm/elfinterp.c 2005-01-11 23:59:21.000000000 -0800 +++ uClibc-0.9.27/ldso/ldso/arm/elfinterp.c 2005-08-13 16:08:19.061345947 -0700 @@ -128,7 +128,7 @@ rel_addr = (ELF_RELOC *) (tpnt->dynamic_info[DT_JMPREL] + tpnt->loadaddr); - this_reloc = rel_addr + (reloc_entry >> 3); + this_reloc = rel_addr + reloc_entry; reloc_type = ELF32_R_TYPE(this_reloc->r_info); symtab_index = ELF32_R_SYM(this_reloc->r_info); @@ -149,13 +149,20 @@ got_addr = (char **) instr_addr; /* Get the address of the GOT entry */ - new_addr = _dl_find_hash(symname, tpnt->symbol_scope, - tpnt, ELF_RTYPE_CLASS_PLT); - if (unlikely(!new_addr)) { - _dl_dprintf(2, "%s: can't resolve symbol '%s'\n", - _dl_progname, symname); - _dl_exit(1); - }; + new_addr = _dl_find_hash(symname, tpnt->symbol_scope, tpnt, + ELF_RTYPE_CLASS_PLT+ELF_RTYPE_CLASS_OF(STT_FUNC)); + if (!new_addr) { + new_addr = _dl_find_hash(symname, tpnt->symbol_scope, tpnt, + ELF_RTYPE_CLASS_PLT+ELF_RTYPE_CLASS_OF(STT_ARM_TFUNC)); + if (new_addr) { + /* Fix up the address for thumb. */ + new_addr = (char*)((unsigned long)new_addr | 1); + } else { + _dl_dprintf(2, "%s: can't resolve symbol '%s'\n", + _dl_progname, symname); + _dl_exit(1); + } + } #if defined (__SUPPORT_LD_DEBUG__) if ((unsigned long) got_addr < 0x40000000) { @@ -278,7 +285,8 @@ if (symtab_index) { symbol_addr = (unsigned long) _dl_find_hash(strtab + symtab[symtab_index].st_name, - scope, tpnt, elf_machine_type_class(reloc_type)); + scope, tpnt, elf_machine_type_class(reloc_type) + + ELF_RTYPE_CLASS_DEFAULT + ELF_RTYPE_CLASS_OF(STT_ARM_TFUNC)); /* * We want to allow undefined references to weak symbols - this might --- uClibc-0.9.27/ldso/ldso/dl-hash.c 2005-01-11 23:59:21.000000000 -0800 +++ uClibc-0.9.27/ldso/ldso/dl-hash.c 2005-08-12 18:28:05.000000000 -0700 @@ -148,7 +148,11 @@ char *weak_result = NULL; elf_hash_number = _dl_elf_hash(name); - + /* The type class argument may specify the valid symbol types, if not + * any type <= STT_FUNC is permitted. + */ + if ((type_class & ELF_RTYPE_CLASS_ALL) == 0) + type_class += ELF_RTYPE_CLASS_DEFAULT; for (; rpnt; rpnt = rpnt->next) { tpnt = rpnt->dyn; @@ -178,13 +182,16 @@ for (si = tpnt->elf_buckets[hn]; si != STN_UNDEF; si = tpnt->chains[si]) { sym = &symtab[si]; + /*... nb, ELF_RTYPE_CLASS_PLT is, must be, "1" - at least + * it must be for the following to work. + */ if (type_class & (sym->st_shndx == SHN_UNDEF)) continue; - if (_dl_strcmp(strtab + sym->st_name, name) != 0) - continue; if (sym->st_value == 0) continue; - if (ELF32_ST_TYPE(sym->st_info) > STT_FUNC) + if ((ELF_RTYPE_CLASS_OF(ELF32_ST_TYPE(sym->st_info)) & type_class) == 0) + continue; + if (_dl_strcmp(strtab + sym->st_name, name) != 0) continue; switch (ELF32_ST_BIND(sym->st_info)) { --- uClibc-0.9.27/libc/sysdeps/linux/arm/clone.S 2005-01-11 23:59:21.000000000 -0800 +++ uClibc-0.9.27/libc/sysdeps/linux/arm/clone.S 2005-08-13 11:56:47.275679748 -0700 @@ -49,12 +49,13 @@ swi __NR_clone movs a1, a1 blt __syscall_error (PLT) - movne pc, lr + bxne lr @ pick the function arg and call address off the stack and execute ldr r0, [sp, #4] + ldr ip, [sp] mov lr, pc - ldr pc, [sp] + bx ip @ and we are done, passing the return value through r0 b _exit (PLT) @@ -70,7 +71,7 @@ /* return -1 */ mvn r0, $0 - mov pc, lr + bx lr .size __clone,.-__clone; .L4: .word errno --- uClibc-0.9.27/libc/sysdeps/linux/arm/mmap64.S 2005-01-11 23:59:21.000000000 -0800 +++ uClibc-0.9.27/libc/sysdeps/linux/arm/mmap64.S 2005-08-13 12:20:35.633560643 -0700 @@ -44,7 +44,7 @@ mov ip, r0 swi __NR_mmap2 cmn r0, $4096 - ldmccfd sp!, {r4, r5, pc} + ldmccfd sp!, {r4, r5, pc} @ requires >=5T cmn r0, $ENOSYS ldmnefd sp!, {r4, r5, lr} bne __syscall_error (PLT) @@ -71,7 +71,7 @@ /* return -1 */ mvn r0, $0 - mov pc, lr + bx lr .size mmap64,.-mmap64; .L4: .word errno --- uClibc-0.9.27/libc/sysdeps/linux/arm/vfork.S 2005-01-11 23:59:21.000000000 -0800 +++ uClibc-0.9.27/libc/sysdeps/linux/arm/vfork.S 2005-08-13 12:23:27.500375540 -0700 @@ -37,7 +37,7 @@ #ifdef __NR_vfork swi __NR_vfork cmn r0, #4096 - movcc pc, lr + bxcc lr /* Check if vfork even exists. */ ldr r1, =-ENOSYS @@ -50,7 +50,7 @@ cmn r0, #4096 /* Syscal worked. Return to child/parent */ - movcc pc, lr + bxcc lr __syscall_error: @@ -64,7 +64,7 @@ /* return -1 */ mvn r0, $0 - mov pc, lr + bx lr .L4: .word errno