RTOS/rtems
1
0
Fork 0
forked from Imagelibrary/rtems
Code Pull Requests Activity

cpukit/libdl/arm: Obey instruction encoding requirements for Thumb BLX

Browse Source 
Calls from Thumb code into ARM code require the use of a BLX instruction
and an optional offset prefix instruction. The BLX instruction encoding
requires that the least significant bit be 0 in all cases while the BL
instruction for Thumb-to-Thumb calls includes that bit as part of the
offset. This ensures that bit 0 of the BLX is set to 0 as required by
the instruction encoding specification.
This commit is contained in:
Kinsey Moore
2024-09-17 14:43:23 -05:00
committed by Kinsey Moore
parent 7cda579524
commit 701e8b2d63
1 changed files with 11 additions and 4 deletions
Download Patch File Download Diff File Expand all files Collapse all files

15
cpukit/libdl/rtl-mdreloc-arm.c
View File

@@ -470,14 +470,21 @@ rtems_rtl_elf_reloc_rel (rtems_rtl_obj* obj,
}
if (!parsing) {
uint16_t bl_tmp;
sign = (tmp >> 24) & 1;
*(uint16_t *)where = (uint16_t)((upper_insn & 0xf800) | (sign << 10) |
((tmp >> 12) & 0x3ff));
*((uint16_t *)where + 1) = (uint16_t)((lower_insn & 0xd000)|
((sign ^ (~(tmp >> 23) & 1)) << 13) |
((sign ^ (~(tmp >> 22) & 1)) << 11) |
((tmp >> 1) & 0x7ff));
bl_tmp = (uint16_t)((lower_insn & 0xd000)|
((sign ^ (~(tmp >> 23) & 1)) << 13) |
((sign ^ (~(tmp >> 22) & 1)) << 11) |
((tmp >> 1) & 0x7ff));
/* Thumb jumps to ARM mode must have 0 in the LSB of the BLX */
if ((bl_tmp & 0xf000) == 0xe000) {
bl_tmp &= 0xfffe;
}
*((uint16_t *)where + 1) = bl_tmp;
if (rtems_rtl_trace (RTEMS_RTL_TRACE_RELOC)){
printf ("rtl: THM_CALL/JUMP24 %p @ %p in %s\n",