--- 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