diff options
Diffstat (limited to 'gas/config/tc-arm.c')
| -rw-r--r-- | gas/config/tc-arm.c | 33 |
1 files changed, 32 insertions, 1 deletions
diff --git a/gas/config/tc-arm.c b/gas/config/tc-arm.c index 9843e1f..e5f0c13 100644 --- a/gas/config/tc-arm.c +++ b/gas/config/tc-arm.c @@ -8424,7 +8424,38 @@ arm_frob_label (sym) ARM_SET_INTERWORK (sym, support_interwork); #endif - if (label_is_thumb_function_name) + /* Note - do not allow local symbols (.Lxxx) to be labeled + as Thumb functions. This is because these labels, whilst + they exist inside Thumb code, are not the entry points for + possible ARM->Thumb calls. Also, these labels can be used + as part of a computed goto or switch statement. eg gcc + can generate code that looks like this: + + ldr r2, [pc, .Laaa] + lsl r3, r3, #2 + ldr r2, [r3, r2] + mov pc, r2 + + .Lbbb: .word .Lxxx + .Lccc: .word .Lyyy + ..etc... + .Laaa: .word Lbbb + + The first instruction loads the address of the jump table. + The second instruction converts a table index into a byte offset. + The third instruction gets the jump address out of the table. + The fourth instruction performs the jump. + + If the address stored at .Laaa is that of a symbol which has the + Thumb_Func bit set, then the linker will arrange for this address + to have the bottom bit set, which in turn would mean that the + address computation performed by the third instruction would end + up with the bottom bit set. Since the ARM is capable of unaligned + word loads, the instruction would then load the incorrect address + out of the jump table, and chaos would ensue. */ + if (label_is_thumb_function_name + && (S_GET_NAME (sym)[0] != '.' || S_GET_NAME (sym)[1] != 'L') + && (bfd_get_section_flags (stdoutput, now_seg) & SEC_CODE) != 0) { /* When the address of a Thumb function is taken the bottom bit of that address should be set. This will allow |