path: root/recipes/uclibc/uclibc-0.9.28/thumb-resolve.patch

# This change reimplements the ARM _dl_linux_resolve entry point - this is
# called to resolve DLL PLT entries.  The assembler is changed to be thumb
# compatible and slightly faster, the C function, _dl_linux_resolver (note
# the extra r) is changed to take a byte address in place of an 8 byte
# count (faster in caller and callee, and slightly easier to understand).
#
--- uClibc-0.9.28/.pc/thumb-resolve.patch/ldso/ldso/arm/elfinterp.c	2005-08-17 15:49:41.000000000 -0700
+++ uClibc-0.9.28/ldso/ldso/arm/elfinterp.c	2005-09-17 12:55:26.379172744 -0700
@@ -55,7 +55,7 @@
 
 	rel_addr = (ELF_RELOC *) tpnt->dynamic_info[DT_JMPREL];
 
-	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);
 
@@ -84,7 +84,9 @@
 		_dl_exit(1);
 	};
 #if defined (__SUPPORT_LD_DEBUG__)
+#if !defined __SUPPORT_LD_DEBUG_EARLY__
 	if ((unsigned long) got_addr < 0x40000000)
+#endif
 	{
 		if (_dl_debug_bindings)
 		{
--- uClibc-0.9.28/.pc/thumb-resolve.patch/ldso/ldso/arm/resolve.S	2005-08-17 15:49:41.000000000 -0700
+++ uClibc-0.9.28/ldso/ldso/arm/resolve.S	2005-09-17 11:02:27.860627464 -0700
@@ -1,43 +1,163 @@
 /*
- * 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
+#include <sys/syscall.h>
 
 .text
+.align 4	@ 16 byte boundary and there are 32 bytes below (arm case)
+#if !defined(__thumb__)
+.arm
 .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}
+#if defined(__THUMB_INTERWORK__)
+	bx    ip
+#else
+	mov   pc, ip
+#endif
+.size _dl_linux_resolve, .-_dl_linux_resolve
+#else
+	@ In the thumb case _dl_linux_resolver is thumb.  If a bl is used
+	@ from arm code the linker will insert a stub call which, with
+	@ binutils 2.16, is not PIC.  Since this code is accessed by an
+	@ ldr pc the reasonable fix is to make _dl_linux_resolve thumb too.
+.thumb
+.globl _dl_linux_resolve
+.thumb_func
+.type _dl_linux_resolve,%function
+
+_dl_linux_resolve:
+	@ _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.
+	push	{r0-r3}
+	mov	r1, lr		@ &GOT_TABLE[2]
+	sub	r0, r1, #4
+	mov	r2, ip		@ &GOT[n]
+	ldr	r0, [r0]	@ r0 := GOT_TABLE[1]
+	@ for the function call r1 := n-3
+	sub	r1, r2
+	asr	r1, r1, #2
+	mvn	r1, r1		@ exactly as in the arm code above
+
+	bl	_dl_linux_resolver
+
+	@ r0 contains the branch address, the return address is above
+	@ the saved r0..r3
+	mov	ip, r0
+	ldr	r1, [sp, #16]
+	mov	lr, r1
+	pop	{r0-r3}
+	add	sp, #4
+	bx	ip
+
 .size _dl_linux_resolve, .-_dl_linux_resolve
+#endif
--- uClibc-0.9.28/.pc/thumb-resolve.patch/ldso/ldso/dl-hash.c	2005-08-17 15:49:41.000000000 -0700
+++ uClibc-0.9.28/ldso/ldso/dl-hash.c	2005-09-21 18:56:31.181689732 -0700
@@ -182,28 +182,52 @@
 		strtab = (char *) (tpnt->dynamic_info[DT_STRTAB]);
 
 		for (si = tpnt->elf_buckets[hn]; si != STN_UNDEF; si = tpnt->chains[si]) {
+			char *result;
 			sym = &symtab[si];
 
-			if (type_class & (sym->st_shndx == SHN_UNDEF))
+			if (sym->st_shndx == SHN_UNDEF)
 				continue;
-			if (_dl_strcmp(strtab + sym->st_name, name) != 0)
+			if (ELF_ST_TYPE(sym->st_info) > STT_FUNC
+#if defined(__arm__) || defined(__thumb__)
+				/* On ARM (only) STT_ARM_TFUNC is a function
+				 * and has a value >STT_FUNC, so this must
+				 * be checked specially.
+				 */
+				&& ELF_ST_TYPE(sym->st_info) != STT_ARM_TFUNC
+#endif
+			   )
 				continue;
-			if (sym->st_value == 0)
+			if (_dl_strcmp(strtab + sym->st_name, name) != 0)
 				continue;
-			if (ELF_ST_TYPE(sym->st_info) > STT_FUNC)
+#if 0
+			/* I don't know how to write this test - need to test shndx
+			 * to see if it is the PLT for this module.
+			 */
+			if ((type_class & ELF_RTYPE_CLASS_PLT) && some test)
 				continue;
+#endif
 
+#if defined(__arm__) || defined(__thumb__)
+			/* On ARM the caller needs to know that STT_ARM_TFUNC
+			 * is a thumb function call, this is now indicated by
+			 * setting the low bit of the value (and newer binutils
+			 * will do this and record STT_FUNC).
+			 */
+			result = (char*)tpnt->loadaddr + (sym->st_value |
+				(ELF_ST_TYPE(sym->st_info) == STT_ARM_TFUNC));
+#else
+			result = (char*)tpnt->loadaddr + sym->st_value;
+#endif
 			switch (ELF_ST_BIND(sym->st_info)) {
 			case STB_WEAK:
-#if 0
-/* Perhaps we should support old style weak symbol handling
- * per what glibc does when you export LD_DYNAMIC_WEAK */
+				/* Record for use later if we can't find a global. */
 				if (!weak_result)
-					weak_result = (char *)tpnt->loadaddr + sym->st_value;
+					weak_result = result;
 				break;
-#endif
+
 			case STB_GLOBAL:
-				return (char*)tpnt->loadaddr + sym->st_value;
+				return result;
+
 			default:	/* Local symbols not handled here */
 				break;
 			}