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| author | David Phillips <david@sighup.nz> | 2019-07-31 21:14:10 +1200 |
|---|---|---|
| committer | David Phillips <david@sighup.nz> | 2019-08-03 12:44:12 +1200 |
| commit | 29b3d80cbef66de71b4db909df78e0853fc1c5b3 (patch) | |
| tree | 5932b20980a9021eae33c6c2bf4c9b6c36ee652e | |
| parent | c836b81b2ee2ecb828c0fa0caecdf91b208dc43d (diff) | |
| download | toy-cpu-assembler-29b3d80cbef66de71b4db909df78e0853fc1c5b3.tar.xz | |
Fix disasm treatment of branch offsets
This patch makes the disassembler treat branch offsets as PC-relative rather
than absolute.
| -rw-r--r-- | disassembler.c | 13 |
1 files changed, 9 insertions, 4 deletions
diff --git a/disassembler.c b/disassembler.c index 24bbc50..ea370ba 100644 --- a/disassembler.c +++ b/disassembler.c @@ -60,11 +60,12 @@ int disasm_jreg(uint16_t i, uint16_t unused) return 0; } -int disasm_bimm(uint16_t i, uint16_t unused) +int disasm_bimm(uint16_t i, uint16_t pc) { const char *inst = get_asm_from_b(GET_JB_COND(i)); - /* FIXME immediate value is meant to be signed */ - printf("%s 0x%x\n", inst, GET_B_OFFSET(i)); + struct {signed int s:10;} sign; + int offset = sign.s = GET_B_OFFSET(i); + printf("%s 0x%x\n", inst, pc + 2 * offset); return 0; } @@ -81,6 +82,7 @@ int disasm(FILE *f) size_t offs = 0; size_t extra_read = 0; uint16_t inst = 0; + uint16_t extra_arg = 0; uint8_t c[2] = { 0 }; int (*disasm_inst)(uint16_t, uint16_t); @@ -100,6 +102,7 @@ int disasm(FILE *f) break; } extra_read = sizeof(c); + extra_arg = c[0] << 16 | c[1]; disasm_inst = disasm_witype; break; case INST_TYPE_JTYPE: @@ -110,6 +113,7 @@ int disasm(FILE *f) */ if (inst & MASK_IS_BRANCH) { disasm_inst = disasm_bimm; + extra_arg = offs; } else { if (inst & MASK_JR) { disasm_inst = disasm_jreg; @@ -118,6 +122,7 @@ int disasm(FILE *f) ret = -errno; break; } + extra_arg = c[0] << 16 | c[1]; extra_read = sizeof(c); disasm_inst = disasm_jimm; } @@ -133,7 +138,7 @@ int disasm(FILE *f) break; } printf("%04x:\t", offs); - ret = disasm_inst(inst, c[0] << 8 | c[1]); + ret = disasm_inst(inst, extra_arg); if (ret < 0) { fprintf(stderr, "Error handling instruction at byte %zd\n", offs); break; |