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authorChristian Krinitsin <mail@krinitsin.com>2025-06-30 12:24:58 +0000
committerChristian Krinitsin <mail@krinitsin.com>2025-06-30 12:27:06 +0000
commit33606b41d35115f887ea688b1a16f2ff85bf2fe4 (patch)
tree406b2c7b19a087ba437c68f3dbf0b589fa1d6150 /results/scraper/launchpad-without-comments/1841442
parentadedf8771bc4de3113041ca21bd4d0d1c0014b6a (diff)
downloadqemu-analysis-33606b41d35115f887ea688b1a16f2ff85bf2fe4.tar.gz
qemu-analysis-33606b41d35115f887ea688b1a16f2ff85bf2fe4.zip
add launchpad bug reports without comments
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+floating point emulation can fail to set FE_INEXACT
+
+Floating point emulation can fail to set FE_INEXACT in some circumstances. This shows up quite often in glibc's "math" tests.  A similar test is attached.
+
+On ppc64le native:
+--
+$ gcc nextafter.c -o nextafter -lm
+$ ./nextafter $(./nextafter)
+0x0000000000000001 0.000000
+0x0
+
+0xa000000
+FE_INEXACT FE_UNDERFLOW
+0x0000000000000000 0.000000
+--
+
+On x86_64:
+--
+$ gcc nextafter.c -o nextafter -lm
+$ ./nextafter $(./nextafter)
+0x0000000000000001 0.000000
+0x0
+
+0x30
+FE_INEXACT FE_UNDERFLOW 
+0x0000000000000000 0.000000
+--
+
+Using qemu-system-ppc64
+--
+$ ./nextafter $(./nextafter)
+0x0000000000000001 0.000000
+0x0
+
+0x8000000
+FE_UNDERFLOW 
+0x0000000000000000 0.000000
+--
+
+Using qemu-x86_64:
+--
+$ ./nextafter $(./nextafter)
+0x0000000000000001 0.000000
+0x0
+
+0x0
+
+0x0000000000000000 0.000000
+--
+
+QEMU versions vary, but not too much, and are pretty close to git HEAD:
+- 586f3dced9 (HEAD -> master, origin/master, origin/HEAD) Merge remote-tracking branch 'remotes/cohuck/tags/s390x-20190822' into staging
+- 864ab31 Update version for v4.1.0-rc4 release
+
+Since the issue happens nearly identically on different targets, I suspect the issue lies somewhere in fpu/softfloat.c.
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