This is forwarded from PR58660
(<http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58660>). Please CC me on
replies as I am not on the list.
In doing some testing of GCC 4.7.3 on a target with an ARMv4T CPU (e.g.
ARM7T or ARM9) I encountered a problem if using Thumb mode with
interworking disabled. For that, obviously I had to created a libgcc
multilib for this combination; for example: -mcpu=arm9 -mthumb
-mno-thumb-interwork.
However this fails to work in GCC 4.7.3 because of a problem in libgcc
making it fail to handle modes correctly for non-interworking operation. A
specific example is aeabi_uldivmod in bpabi.S which is an ARM (not thumb)
function, which includes a bl to __gnu_uldivmod_helper.
__gnu_uldivmod_helper is from bpabi.c and is in Thumb mode.
The linker helpfully adds a little trampoline to switch to Thumb mode
with the bx instruction (____gnu_uldivmod_helper_from_arm). However GCC
returns from __gnu_uldivmod_helper with:
pop {r3, r4, r5, r6, r7, pc}
This means that no mode switch happens on the return from the Thumb mode
function to the ARM mode aeabi_uldivmod function.
I am attaching a potential fix for the problem with aeabi_ldivmod and
aeabi_uldivmod (against 4.7.3), so it would be good for that to be applied
at least, including on the 4.7 and 4.8 branches.
2013-10-07 Jonathan Larmour <j...@ecoscentric.com>
* config/arm/bpabi.S (aeabi_ldivmod, aeabi_uldivmod): Allow for
non-interworking Thumb builds.
Someone may also want to double-check whether this sort of problem may
apply to other functions (although I haven't found any others yet myself,
but I'm not sure about how functions like those in unaligned-funcs.c would
be called).
Thanks,
Jifl
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------["Si fractum non sit, noli id reficere"]------ Opinions==mine
diff -x CVS -x .svn -x '*~' -x '.#*' -x autom4te.cache -urpN
gcc-4.7.3.pre/libgcc/config/arm/bpabi.S gcc-4.7.3/libgcc/config/arm/bpabi.S
--- gcc-4.7.3.pre/libgcc/config/arm/bpabi.S 2011-11-02 15:03:19.000000000
+0000
+++ gcc-4.7.3/libgcc/config/arm/bpabi.S 2013-10-07 23:39:05.508083589 +0100
@@ -133,10 +133,25 @@ ARM_FUNC_START aeabi_ldivmod
#else
do_push {sp, lr}
#endif
+#if defined(__INTERWORKING_STUBS__)
+ /* In this case, __gnu_ldivmod_helper is compiled in Thumb mode, but
+ without interworking. This means it needs to be called in Thumb
+ mode, and will return in Thumb mode, not ARM. So we handle that. */
+ orr ip, pc, #1
+ bx ip
+ .code 16
+ bl SYM(__gnu_ldivmod_helper) __PLT__
+ ldr r2, [sp, #4]
+ mov lr, r2
+ ldr r2, [sp, #8]
+ ldr r3, [sp, #12]
+ add sp, sp, #16
+#else
bl SYM(__gnu_ldivmod_helper) __PLT__
ldr lr, [sp, #4]
add sp, sp, #8
do_pop {r2, r3}
+#endif
RET
#endif /* L_aeabi_ldivmod */
@@ -153,10 +168,25 @@ ARM_FUNC_START aeabi_uldivmod
#else
do_push {sp, lr}
#endif
+#if defined(__INTERWORKING_STUBS__)
+ /* In this case, __gnu_uldivmod_helper is compiled in Thumb mode, but
+ without interworking. This means it needs to be called in Thumb
+ mode, and will return in Thumb mode, not ARM. So we handle that. */
+ orr ip, pc, #1
+ bx ip
+ .code 16
+ bl SYM(__gnu_uldivmod_helper) __PLT__
+ ldr r2, [sp, #4]
+ mov lr, r2
+ ldr r2, [sp, #8]
+ ldr r3, [sp, #12]
+ add sp, sp, #16
+#else
bl SYM(__gnu_uldivmod_helper) __PLT__
ldr lr, [sp, #4]
add sp, sp, #8
do_pop {r2, r3}
+#endif
RET
#endif /* L_aeabi_divmod */
