* [Bug translator/27829] New: support for floating point values passed through sdt.h markers
@ 2021-05-07 2:06 fche at redhat dot com
2021-10-19 18:43 ` [Bug translator/27829] " scox at redhat dot com
0 siblings, 1 reply; 2+ messages in thread
From: fche at redhat dot com @ 2021-05-07 2:06 UTC (permalink / raw)
To: systemtap
https://sourceware.org/bugzilla/show_bug.cgi?id=27829
Bug ID: 27829
Summary: support for floating point values passed through sdt.h
markers
Product: systemtap
Version: unspecified
Status: NEW
Severity: normal
Priority: P2
Component: translator
Assignee: systemtap at sourceware dot org
Reporter: fche at redhat dot com
Target Milestone: ---
Created attachment 13422
--> https://sourceware.org/bugzilla/attachment.cgi?id=13422&action=edit
partial patch
While stap has recently developed the ability access floating point parameters
passed through dwarf-designated locations, we can't do that for sdt.h. That's
for a couple of reasons:
- tapsets.cxx sdt_uprobe_var_expanding_visitor::build_dwarf_registers does not
recognize FP register names
- includes/sys/sdt.h uses an STAP_SDT_ARG_CONSTRAINT that excludes FP registers
(so FP values are copied into integer registers anyway)
- includes/sys/sdt.h has no way of marking up floating-point vs integer
registers
A partial patch for the first two parts is attached, for x86-64.
The latter requires some coordination with other sdt.h consumers, in order to
parse a modification of the operand description syntax. One possibility:
Instead of:
% readelf -n stap
stapsdt 0x0000003b NT_STAPSDT (SystemTap probe descriptors)
[...]
Arguments: 8@%xmm0 4@%xmm1
use:
stapsdt 0x0000003b NT_STAPSDT (SystemTap probe descriptors)
[...]
Arguments: 8f@%xmm0 4f@%xmm1
i.e., insert an "f" char between the length and the "@" sign. We could/should
do that even if the floats were copied into an integer register due to operand
constraints.
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2021-05-07 2:06 [Bug translator/27829] New: support for floating point values passed through sdt.h markers fche at redhat dot com
2021-10-19 18:43 ` [Bug translator/27829] " scox at redhat dot com
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