* [Bug libc/1468] AMD64 {get,set,swap,make}context use wrong offsets into ucontext_t
2005-10-12 5:21 [Bug libc/1468] New: AMD64 {get,set,swap,make}context use wrong offsets into ucontext_t nmiell at comcast dot net
@ 2005-10-12 5:21 ` nmiell at comcast dot net
2005-10-12 5:59 ` nmiell at comcast dot net
` (3 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: nmiell at comcast dot net @ 2005-10-12 5:21 UTC (permalink / raw)
To: glibc-bugs
------- Additional Comments From nmiell at comcast dot net 2005-10-12 05:21 -------
Created an attachment (id=698)
--> (http://sourceware.org/bugzilla/attachment.cgi?id=698&action=view)
correct the ucontext offsets
--
http://sourceware.org/bugzilla/show_bug.cgi?id=1468
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^ permalink raw reply [flat|nested] 6+ messages in thread* [Bug libc/1468] AMD64 {get,set,swap,make}context use wrong offsets into ucontext_t
2005-10-12 5:21 [Bug libc/1468] New: AMD64 {get,set,swap,make}context use wrong offsets into ucontext_t nmiell at comcast dot net
2005-10-12 5:21 ` [Bug libc/1468] " nmiell at comcast dot net
@ 2005-10-12 5:59 ` nmiell at comcast dot net
2005-10-14 16:31 ` drepper at redhat dot com
` (2 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: nmiell at comcast dot net @ 2005-10-12 5:59 UTC (permalink / raw)
To: glibc-bugs
------- Additional Comments From nmiell at comcast dot net 2005-10-12 05:59 -------
Even with this patch, the the context functions still use the wrong offsets.
The problem is that FNSTENV and FLDENV operate on memory with the following layout:
struct fpenv
{
uint16_t cwd;
uint16_t __pad0;
uint16_t swd;
uint16_t __pad1;
uint16_t ftw;
uint16_t __pad2;
uint32_t eip;
uint16_t cs;
uint16_t opcode;
uint32_t edi;
uint16_t ds;
uint16_t __pad3
};
while struct _libc_fpstate uses the 64-bit FXSAVE/FXRSTOR format, which starts
like this:
struct _libc_fpstate
{
__uint16_t cwd;
__uint16_t swd;
__uint16_t ftw;
__uint16_t fop;
__uint64_t rip;
__uint64_t rdp;
__uint32_t mxcsr;
/* ... */
}
Which means that the existing code which does FNSTENV to uc.__fpregs_mem will
store members in the wrong locations and will corrupt the saved %mxcsr (assuming
the struct offsets in ucontext_i.h are corrected without any other updates to
the context functions).
--
http://sourceware.org/bugzilla/show_bug.cgi?id=1468
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^ permalink raw reply [flat|nested] 6+ messages in thread* [Bug libc/1468] AMD64 {get,set,swap,make}context use wrong offsets into ucontext_t
2005-10-12 5:21 [Bug libc/1468] New: AMD64 {get,set,swap,make}context use wrong offsets into ucontext_t nmiell at comcast dot net
2005-10-12 5:21 ` [Bug libc/1468] " nmiell at comcast dot net
2005-10-12 5:59 ` nmiell at comcast dot net
@ 2005-10-14 16:31 ` drepper at redhat dot com
2005-10-15 3:27 ` nmiell at comcast dot net
2005-10-16 8:23 ` drepper at redhat dot com
4 siblings, 0 replies; 6+ messages in thread
From: drepper at redhat dot com @ 2005-10-14 16:31 UTC (permalink / raw)
To: glibc-bugs
------- Additional Comments From drepper at redhat dot com 2005-10-14 16:31 -------
Fix in the CVS trunk version.
--
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |RESOLVED
Resolution| |FIXED
http://sourceware.org/bugzilla/show_bug.cgi?id=1468
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^ permalink raw reply [flat|nested] 6+ messages in thread* [Bug libc/1468] AMD64 {get,set,swap,make}context use wrong offsets into ucontext_t
2005-10-12 5:21 [Bug libc/1468] New: AMD64 {get,set,swap,make}context use wrong offsets into ucontext_t nmiell at comcast dot net
` (2 preceding siblings ...)
2005-10-14 16:31 ` drepper at redhat dot com
@ 2005-10-15 3:27 ` nmiell at comcast dot net
2005-10-16 8:23 ` drepper at redhat dot com
4 siblings, 0 replies; 6+ messages in thread
From: nmiell at comcast dot net @ 2005-10-15 3:27 UTC (permalink / raw)
To: glibc-bugs
------- Additional Comments From nmiell at comcast dot net 2005-10-15 03:27 -------
Sorry, I should have marked my patch as obsolete when I added comment #2.
Fortunately, I was wrong and the MXCSR register isn't actually corrupted --
STMXCSR occurs after FNSTENV, so the saved %ds and padding are overwritten by
the saved %mxcsr, but they're purely informational and don't effect execution
when they're loaded by FLDENV (afaik). (Meaning no new bugs were introduced, I
think.)
I was just going to submit a patch to setcontext, getcontext and swapcontext
that makes them use FXSAVE and FXRSTOR instead of FNSTENV/STMXCSR and
FLDENV/LDMXCSR -- it turns out that saving and restoring the entire FPU state
with these intructions is faster than just saving/restoring the x87 environment
and MXCSR register and FXSAVE/FXRSTOR would naturally put things in the right
place in struct _libc_fpstate.
However, I ran into a problem that I don't know how to solve:
The FXSAVE area needs to be 16-byte aligned, however the natural alignment of
struct _libc_fpstate is 8. As such, the __fpregs_mem member of struct ucontext
isn't aligned sufficiently for use with the FXSAVE and FXRSTOR instructions.
_libc_fpstate should probably get an __attribute__((aligned(16))), but this
would change the layout of struct ucontext and definately break the ABI.
--
What |Removed |Added
----------------------------------------------------------------------------
Status|RESOLVED |REOPENED
Resolution|FIXED |
http://sourceware.org/bugzilla/show_bug.cgi?id=1468
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^ permalink raw reply [flat|nested] 6+ messages in thread* [Bug libc/1468] AMD64 {get,set,swap,make}context use wrong offsets into ucontext_t
2005-10-12 5:21 [Bug libc/1468] New: AMD64 {get,set,swap,make}context use wrong offsets into ucontext_t nmiell at comcast dot net
` (3 preceding siblings ...)
2005-10-15 3:27 ` nmiell at comcast dot net
@ 2005-10-16 8:23 ` drepper at redhat dot com
4 siblings, 0 replies; 6+ messages in thread
From: drepper at redhat dot com @ 2005-10-16 8:23 UTC (permalink / raw)
To: glibc-bugs
------- Additional Comments From drepper at redhat dot com 2005-10-16 08:23 -------
There is no reason to reopen the bug. It's fixed, and no changes to the data
types can be made.
--
What |Removed |Added
----------------------------------------------------------------------------
Status|REOPENED |RESOLVED
Resolution| |FIXED
http://sourceware.org/bugzilla/show_bug.cgi?id=1468
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