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ed0816bd93
When linking the following code
.global _prog_start
_prog_start:
mv x1, x1
mv x2, x2
.align 2
rvc_boundry:
.option norvc
.align 3
mv x3, x3
we currently emit an invalid two-byte 0 instruction. The actual output
code looks like
0000000080000000 <_prog_start>:
80000000: 8086 mv ra,ra
80000002: 810a mv sp,sp
0000000080000004 <rvc_boundry>:
80000004: 0000 unimp
80000006: 0001 nop
80000008: 00018193 mv gp,gp
This ends up manifesting due to the two-byte compressed NOP that's
pessimisticly emitted by the ".align 2", which results in "rvc_boundry"
being 2-byte aligned. frag_align_code() then goes and outputs a 2-byte
NOP (which is invalid in no-RVC mode) to align the code back to a 4-byte
boundry, which can't be relaxed away by the linker as it's not part of
the R_RISCV_RELAX relocation.
The fix is to just always emit the worst case possible alignment into
the output as a single R_RISCV_RELAX, which the linker will then fix up.
With this patch I get the expected code generation
0000000080000000 <_prog_start>:
80000000: 8086 mv ra,ra
80000002: 810a mv sp,sp
0000000080000004 <rvc_boundry>:
80000004: 00000013 nop
80000008: 00018193 mv gp,gp
gas/ChangeLog
2017-09-07 Palmer Dabbelt <palmer@dabbelt.com>
* config/tc-riscv.c (riscv_frag_align_code): Emit the entire
alignment sequence inside R_RISCV_ALIGN.
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