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| author | Christian Krinitsin <mail@krinitsin.com> | 2025-07-07 17:23:11 +0000 |
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| committer | Christian Krinitsin <mail@krinitsin.com> | 2025-07-07 17:23:11 +0000 |
| commit | c50b0c4da17b6e83640e4ed2380fffb5f507c846 (patch) | |
| tree | b4f203fce1380e2ea3578a784bb8ee060fe42cbd /results/classifier/zero-shot-user-mode/output/instruction/2495 | |
| parent | 61361f925d4914a6608a0076e64cc2399311ed5f (diff) | |
| download | emulator-bug-study-c50b0c4da17b6e83640e4ed2380fffb5f507c846.tar.gz emulator-bug-study-c50b0c4da17b6e83640e4ed2380fffb5f507c846.zip | |
add zero-shot results
Diffstat (limited to 'results/classifier/zero-shot-user-mode/output/instruction/2495')
| -rw-r--r-- | results/classifier/zero-shot-user-mode/output/instruction/2495 | 78 |
1 files changed, 78 insertions, 0 deletions
diff --git a/results/classifier/zero-shot-user-mode/output/instruction/2495 b/results/classifier/zero-shot-user-mode/output/instruction/2495 new file mode 100644 index 00000000..60c640f2 --- /dev/null +++ b/results/classifier/zero-shot-user-mode/output/instruction/2495 @@ -0,0 +1,78 @@ +instruction: 0.380 +syscall: 0.314 +runtime: 0.306 + + + +A bug in x86-64 MMX instructions +Description of problem: +It seems QEMU emits invalid TCG when lifting MMX instructions with redundant REX prefixes. For example, when lifting `490f7ec0 (movq r8, mm0)`, QEMU generates the following valid TCG. + +``` + ---- 00000000004011f2 0000000000000000 + call enter_mmx,$0x0,$0,env + ld_i64 loc0,env,$0x270 + mov_i64 r8,loc0 + mov_i64 rip,$0x4011f6 + exit_tb $0x0 + set_label $L0 + exit_tb $0x7f84f82ec143 +``` + +However, after changing the value of the rex prefix to `4f` , so the instruction becomes `4f0f7ec0 (rex.WRXB movq r8, mm0)`, the lifted TCG is changed to: + +``` + ---- 00000000004011f2 0000000000000000 + call enter_mmx,$0x0,$0,env + ld_i64 loc0,env,$0x2f0 // The offset to MM0 is changed + mov_i64 r8,loc0 + mov_i64 rip,$0x4011f6 + exit_tb $0x0 + set_label $L0 + exit_tb $0x7f98e82ec143 +``` + +I have observed this bug in numerous MMX instructions. For example, `410fdaff (rex.B pminub mm7, mm7)` is lifted to the wrong TCGs. + +It seems this bug looks similar to #2474. +Steps to reproduce: +1. Write `test.c` +``` +#include <stdint.h> +#include <stdio.h> +#include <string.h> + +uint8_t i_R8[8] = { 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0 }; +uint8_t i_MM0[8] = { 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff }; +uint8_t o_R8[8]; + +void __attribute__ ((noinline)) show_state() { + printf("R8: "); + for (int i = 0; i < 8; i++) { + printf("%02x ", o_R8[i]); + } + printf("\n"); +} + +void __attribute__ ((noinline)) run() { + __asm__ ( + ".intel_syntax noprefix\n" + "mov r8, qword ptr [rip + i_R8]\n" + "movq mm0, qword ptr [rip + i_MM0]\n" + ".byte 0x4f, 0x0f, 0x7e, 0xc0\n" + "mov qword ptr [rip + o_R8], r8\n" + ".att_syntax\n" + ); +} + +int main(int argc, char **argv) { + run(); + show_state(); + return 0; +} +``` +2. Compile `test.bin` using this command: `gcc-12 -O2 -no-pie ./test.c -o ./test.bin` +3. Run QEMU using this command: `qemu-x86_64 ./test.bin` +4. The program, runs on top of the buggy QEMU, prints the value of R8 as `00 00 00 00 00 00 00 00`. It should print `ff ff ff ff ff ff ff ff` after the bug is fixed. +Additional information: + |