mirror/binutils-gdb
2
0
Fork 0
mirror of https://sourceware.org/git/binutils-gdb.git synced 2024-11-27 03:51:15 +08:00
Code Issues Packages Projects Releases Wiki Activity

doc: sframe: add appendix for generating stack traces

Browse Source 
Add an appendix to provide a rough outline to show how to generate stack
traces using the SFrame format.  Such content should hopefully aid the
reader assimmilate the information in the specification.

libsframe/
	* doc/sframe-spec.texi: Add new appendix.
This commit is contained in:
Indu Bhagat 2024-06-26 12:43:51 -07:00
parent 4de9a5ccd6
commit 604b972e61
1 changed files with 84 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

84
libsframe/doc/sframe-spec.texi
View File

@ -54,6 +54,9 @@ low-overhead mechanism to generate stack traces.
* SFrame Section::
* ABI/arch-specific Definition::
Appendices
* Generating Stack Traces using SFrame::
* Index::
@end menu
@ -823,6 +826,87 @@ Hence, in summary:
@item 3 @tab FP = CFA + offset3
@end multitable
@node Generating Stack Traces using SFrame
@appendix Generating Stack Traces using SFrame
Using some C-like pseudocode, this section highlights how SFrame provides a
simple, fast and low-overhead mechanism to generate stack traces. Needless to
say that for generating accurate and useful stack traces, several other aspects
will need attention: finding and decoding bits of SFrame section(s) in the
program binary, symbolization of addresses, to name a few.
In the current context, a @code{frame} is the abstract construct that
encapsulates the following information:
@itemize @minus
@item
program counter (PC),
@item
stack pointer (SP), and
@item
frame pointer (FP)
@end itemize
With that said, establishing the first @code{frame} should be trivial:
@example
// frame 0
frame->pc = current_IP;
frame->sp = get_reg_value (REG_SP);
frame->fp = get_reg_value (REG_FP);
@end example
where @code{REG_SP} and @code{REG_FP} are are ABI-designated stack pointer and
frame pointer registers respectively.
Next, given frame N, generating stack trace needs us to get frame N+1. This
can be done as follows:
@example
// Get the PC, SP, and FP for frame N.
pc = frame->pc;
sp = frame->sp;
fp = frame->fp;
// Populate frame N+1.
int err = get_next_frame (&next_frame, pc, sp, fp);
@end example
where given the values of the program counter, stack pointer and frame pointer
from frame N, @code{get_next_frame} populates the provided @code{next_frame}
object and returns the error code, if any. In the following pseudocode for
@code{get_next_frame}, the @code{sframe_*} functions fetch information from the
SFrame section.
@example
fre = sframe_find_fre (pc);
if (fre)
// Whether the base register for CFA tracking is REG_FP.
base_reg_val = sframe_fre_base_reg_fp_p (fre) ? fp : sp;
// Get the CFA stack offset from the FRE.
cfa_offset = sframe_fre_get_cfa_offset (fre);
// Get the fixed RA offset or FRE stack offset as applicable.
ra_offset = sframe_fre_get_ra_offset (fre);
// Get the fixed FP offset or FRE stack offset as applicable.
fp_offset = sframe_fre_get_fp_offset (fre);
cfa = base_reg_val + cfa_offset;
next_frame->sp = cfa;
ra_stack_loc = cfa + ra_offset;
// Get the address stored in the stack location.
next_frame->pc = read_value (ra_stack_loc);
if (fp_offset is VALID)
fp_stack_loc = cfa + fp_offset;
// Get the value stored in the stack location.
next_frame->fp = read_value (fp_stack_loc);
else
// Continue to use the value of fp as it has not
// been clobbered by the current frame yet.
next_frame->fp = fp;
else
ret = ERR_NO_SFRAME_FRE;
@end example
@node Index
@unnumbered Index