Bug 136700

Summary:	64-bit PowerPC GDB can't fetch FPSCR
Product:	[Fedora] Fedora	Reporter:	Andrew Cagney <cagney>
Component:	kernel	Assignee:	David Woodhouse <dwmw2>
Status:	CLOSED DUPLICATE	QA Contact:	Brian Brock <bbrock>
Severity:	medium	Docs Contact:
Priority:	medium
Version:	rawhide	CC:	wtogami
Target Milestone:	---
Target Release:	---
Hardware:	powerpc
OS:	Linux
Whiteboard:
Fixed In Version:		Doc Type:	Bug Fix
Doc Text:		Story Points:	---
Clone Of:		Environment:
Last Closed:	2006-02-21 19:06:32 UTC	Type:	---
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:
Bug Depends On:
Bug Blocks:	116894

Description Andrew Cagney 2004-10-21 19:41:42 UTC

GDB can't fetch the PowerPC's FPSCR register: 

  (gdb) print $fpscr
  reading register fpscr (#70): Input/output error.
  (gdb)

as occures when GDB is doing an inferior function call.

Version-Release number of selected component (if applicable):

 2.6.9-rc4

strace shows:

  ptrace(PTRACE_PEEKUSER, 503, 0x288, 0xffffcdb0) = -1 EIO

and grubbing the headers:

  #define PT_FPR0 48
  define PT_FPSCR (PT_FPR0 + 32 + 1)
  (gdb) print/x (48 + 32 + 1) * 8
  $1 = 0x288

suggests that the value is correct.

Comment 1 David Woodhouse 2004-10-25 22:22:33 UTC

See bug #91727. 

The value of PT_FPSCR for 64-bit userspace is different to the value
for 32-bit. This is because a 'double' is worth two longs for 32-bit
code, and only one for 64-bit code.

I think the kernel is doing the right thing -- if there's a kernel bug
it's purely the evilness of the way the interface is done. If we're
going to start criticising the ptrace interface... :)

Closing NOTABUG. Feel free to argue if you feel strongly ;)

Comment 2 Andrew Cagney 2004-10-26 00:53:05 UTC


*** This bug has been marked as a duplicate of 91727 ***

Comment 3 Red Hat Bugzilla 2006-02-21 19:06:32 UTC

Changed to 'CLOSED' state since 'RESOLVED' has been deprecated.