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cpukit/libdl/arm: Add support for trailing Thumb to ARM calls

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This expands the size of an ARM trampoline from 8 bytes to 10 bytes to
support THM_JUMP24 tail calls that require a BX instruction to change
modes.
This commit is contained in:
Kinsey Moore
2024-09-24 14:02:48 -05:00
committed by Kinsey Moore
parent 701e8b2d63
commit 8f8d0c806b
1 changed files with 50 additions and 6 deletions
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56
cpukit/libdl/rtl-mdreloc-arm.c
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@@ -101,11 +101,35 @@ set_veneer(void* tramopline, Elf_Addr target)
return tramp;
}
static void*
set_thumb_bx_veneer(void* tramopline, Elf_Addr target)
{
/*
* http://shell-storm.org/online/Online-Assembler-and-Disassembler/
*
* Thumb mode:
* ldr.w r12, [pc, 4]
* bx r12
* .word target
*
*/
uint16_t* tramp = (uint16_t*) tramopline;
/* ldr.w r12, [pc, 4]*/
*tramp++ = 0xf8df;
*tramp++ = 0xc002;
/* bx r12 */
*tramp++ = 0x4760;
*tramp++ = (uint16_t) target & 0xffff;
*tramp++ = (uint16_t) ((target >> 16) & 0xffff);
return tramp;
}
static size_t
get_veneer_size(int type)
{
(void) type;
return 8;
/* BX veneers need 10 bytes */
return 10;
}
uint32_t rtems_rtl_obj_tramp_alignment (const rtems_rtl_obj* obj)
@@ -423,10 +447,6 @@ rtems_rtl_elf_reloc_rel (rtems_rtl_obj* obj,
else {
if (ELF_R_TYPE(rel->r_info) == R_TYPE(THM_JUMP24)) {
tmp = (tmp + 2) & ~3; /* aligned to 4 bytes only for JUMP24 */
#if !ALLOW_UNTESTED_RELOCS
printf("THM_JUMP24 to arm not supported\n");
return rtems_rtl_elf_rel_failure;
#endif
}
else {
/* THM_CALL bl-->blx */
@@ -443,7 +463,31 @@ rtems_rtl_elf_reloc_rel (rtems_rtl_obj* obj,
tmp = symvalue + addend;
tmp = tmp - (Elf_Addr)where;
if (((Elf_Sword)tmp > 0x7fffff) || ((Elf_Sword)tmp < -0x800000)) {
if (isThumb(symvalue) == false && ELF_R_TYPE(rel->r_info) == R_TYPE(THM_JUMP24)) {
Elf_Word tramp_addr;
size_t tramp_size = get_veneer_size(ELF_R_TYPE(rel->r_info));
if (parsing) {
if (rtems_rtl_trace (RTEMS_RTL_TRACE_RELOC))
printf ("rtl: THM_JUMP24 tramp add: %08x - %p = %i\n",
symvalue + addend, where, (Elf_Sword) tmp);
return rtems_rtl_elf_rel_tramp_add;
}
if (!rtems_rtl_obj_has_tramp_space (obj, tramp_size)) {
rtems_rtl_set_error (EINVAL,
"%s: THM_JUMP24: overflow: no tramp memory",
sect->name);
return rtems_rtl_elf_rel_failure;
}
tramp_addr = (Elf_Addr) obj->tramp_brk;
obj->tramp_brk = set_thumb_bx_veneer(obj->tramp_brk, symvalue);
tmp = tramp_addr + addend;
tmp = tmp - (Elf_Addr)where;
} else if (((Elf_Sword)tmp > 0x7fffff) || ((Elf_Sword)tmp < -0x800000)) {
Elf_Word tramp_addr;
size_t tramp_size = get_veneer_size(ELF_R_TYPE(rel->r_info));