diff options
Diffstat (limited to 'results/classifier/zero-shot-user-mode/output/runtime/618')
| -rw-r--r-- | results/classifier/zero-shot-user-mode/output/runtime/618 | 101 |
1 files changed, 0 insertions, 101 deletions
diff --git a/results/classifier/zero-shot-user-mode/output/runtime/618 b/results/classifier/zero-shot-user-mode/output/runtime/618 deleted file mode 100644 index 6376e77e..00000000 --- a/results/classifier/zero-shot-user-mode/output/runtime/618 +++ /dev/null @@ -1,101 +0,0 @@ -runtime: 0.346 -instruction: 0.345 -syscall: 0.309 - - - -overflow condition code determined incorrectly after subtraction on s390x -Description of problem: -Paul Eggert found this bug, just by taking a look at the file `qemu/target/s390x/tcg/cc_helper.c`. - -The following program -[foo.c](/uploads/c1f425684fd661c4437950d7d8ddf31d/foo.c) -``` -#include <stdio.h> - -int overflow_32 (int x, int y) -{ - int sum; - return __builtin_sub_overflow (x, y, &sum); -} - -int overflow_64 (long long x, long long y) -{ - long sum; - return __builtin_sub_overflow (x, y, &sum); -} - -int a1 = 0; -int b1 = -2147483648; -long long a2 = 0L; -long long b2 = -9223372036854775808L; - -int main () -{ - { - int a = a1; - int b = b1; - printf ("a = 0x%x, b = 0x%x\n", a, b); - printf ("no_overflow = %d\n", ! overflow_32 (a, b)); - } - { - long long a = a2; - long long b = b2; - printf ("a = 0x%llx, b = 0x%llx\n", a, b); - printf ("no_overflow = %d\n", ! overflow_64 (a, b)); - } -} -``` -should print -``` -a = 0x0, b = 0x80000000 -no_overflow = 0 -a = 0x0, b = 0x8000000000000000 -no_overflow = 0 -``` -However, when compiled as an s390x program and executed through qemu 6.1.0 (Linux user-mode), it prints 'no_overflow = 1' twice. -``` -$ s390x-linux-gnu-gcc-10 --version -s390x-linux-gnu-gcc-10 (Ubuntu 10.3.0-1ubuntu1~20.04) 10.3.0 -``` - -``` -$ s390x-linux-gnu-gcc-10 -static foo.c -$ ~/inst-qemu/6.1.0/bin/qemu-s390x a.out -a = 0x0, b = 0x80000000 -no_overflow = 1 -a = 0x0, b = 0x8000000000000000 -no_overflow = 1 -``` - -``` -$ s390x-linux-gnu-gcc-10 -O2 -static foo.c -$ ~/inst-qemu/6.1.0/bin/qemu-s390x a.out -a = 0x0, b = 0x80000000 -no_overflow = 1 -a = 0x0, b = 0x8000000000000000 -no_overflow = 1 -``` - -The code generated by 's390x-linux-gnu-gcc-10 -O2' makes use of the 'o' (overflow / ones) condition code: -``` -overflow_64: - lgr %r1,%r2 ;; copy a into %r1 - lghi %r2,0 - sgr %r1,%r3 ;; subtract b from a - bnor %r14 ;; if no overflow, return %r2 = 0 - lghi %r2,1 - br %r14 ;; otherwise, return %r2 = 1 -``` - -The condition code and the overflow bit are defined in the z/Architecture Principles of Operation (POP) http://publibfi.boulder.ibm.com/epubs/pdf/dz9zr011.pdf page 7-5 / 7-6 / 7-388 : "In mathematical terms, signed addition and subtraction produce a fixed-point overflow when the result is outside the range of representation for signed binary integers." - -I conclude that the bug is in QEMU: QEMU does not set the overflow condition code correctly. -Steps to reproduce: -[foo.static.s390x](/uploads/e4b79b019db590f3a4b13cac41e57ba6/foo.static.s390x) -(the result of "s390x-linux-gnu-gcc-10 -static -O2 foo.c -o foo.static.s390x") - -1. `qemu-s390x foo.static.s390x` -Additional information: -The attached patch fixes it. -[0002-s390x-Fix-determination-of-overflow-condition-code-a.patch](/uploads/8d414f84fe0ed36bf07bd28f5e7836ab/0002-s390x-Fix-determination-of-overflow-condition-code-a.patch) |