I'm using libdw to:
dwarf_getsrclines(&cuDIE, &lineBuffer, &lineCount);
for (size_t i = 0; i < lineCount; i++) {
auto line = dwarf_onesrcline(lineBuffer, i);
dwarf_lineno(line, ¤t_statement.line_number);
const char *file_name = dwarf_linesrc(line, NULL, NULL);
status = dwarf_lineaddr(line, ¤t_statement.start_addr);
// here add line info to our own structure
}
In the previous email I gave you an example for the line 233, which gdb adds
two breakpoints in two different functions. I understand that, because
optimizations, lines can generate scattered instructions.
The following is the start address and corresponding file name for the line 233
that libdw gives me:
> And we find all these locations:
> Compilation Unit name: lulesh.cc
> [403eb0, ffffffffffffffff) /g/g90/devkota1/LULESH/lulesh.cc:233
> [4060a0, ffffffffffffffff) /g/g90/devkota1/LULESH/lulesh.cc:233
> [409c0c, ffffffffffffffff) /g/g90/devkota1/LULESH/lulesh.cc:233
That means the line 233 for that file generated three scattered instruction
blocks. At 403eb0, 4060a0, and 409c0c. But that doesn't mean it's only one
machine instruction. It could be a whole block of instructions. And now I'm
trying to find how to determine the end address for each of them. (the
ffffffffffffffff address is the address I'm trying to find).
Suppose these addresses:
....
403eb0: 48 63 5a 0c movslq 0xc(%rdx),%rbx
403eb4: 4c 63 5a 14 movslq 0x14(%rdx),%r11
403eb8: 4c 63 72 04 movslq 0x4(%rdx),%r14
403ebc: 4c 63 3a movslq (%rdx),%r15
....
4060a0: 41 56 push %r14
4060a2: 48 8b 07 mov (%rdi),%rax
4060a5: 41 55 push %r13
4060a7: 41 54 push %r12
....
409c0c: 49 8b 04 24 mov (%r12),%rax
409c10: 4c 63 3b movslq (%rbx),%r15
409c13: 4c 63 73 04 movslq 0x4(%rbx),%r14
409c17: 4c 63 6b 08 movslq 0x8(%rbx),%r13
Libdw says the line 233 are associated with those three address after the dots
(....): 403eb0, 4060a0, and 409c0c.
But we need to know how far down this association goes. That's what I call
range end.
For my knowledge about it, this information is not encoded in the dwarf_line
state machine instructions. Right? Would you know how to get it?
I know that the state machine will shift line number and address number to
encode instructions such as:
DW_LNS_fixed_advance_pc
SPECIAL(2, 0)
DW_LNS_fixed_advance_pc
SPECIAL(2, 0)
DW_LNS_fixed_advance_pc
SPECIAL(1, 0)
DW_LNS_fixed_advance_pc
SPECIAL(1, 0)
DW_LNS_fixed_advance_pc
DW_LNE_end_sequence
And that does not give us range end. Am I correct? Can we make any assumptions
for it?
Regards,
Sasha
From: Mark Wielaard <m...@klomp.org>
Sent: Thursday, September 12, 2019 4:00 AM
To: Sasha Da Rocha Pinheiro <darochapi...@wisc.edu>
Cc: elfutils-devel@sourceware.org <elfutils-devel@sourceware.org>
Subject: Re: line info
Hi Sasha,
On Wed, Sep 11, 2019 at 09:52:23PM +0000, Sasha Da Rocha Pinheiro wrote:
> how do we get the line info range end address for a given line and file?
I am not sure I understand your question competely. What are you
using to get at the line and file? In theory there is no "range end
address" for a given source file line. The instructions associated
with a particular source code line can be scattered around by various
compiler optimisations.
> For instance, gdb adds 2 breapoint to:
> (gdb) b /g/g90/devkota1/LULESH/lulesh.cc:233
> Breakpoint 1 at 0x4060a0: /g/g90/devkota1/LULESH/lulesh.cc:233. (2 locations)
> (gdb) i b
> Num Type Disp Enb Address What
> 1 breakpoint keep y <MULTIPLE>
> 1.1 y 0x00000000004060a0 in
> CollectDomainNodesToElemNodes(Domain&, Index_t const*, Real_t*, Real_t*,
> Real_t*) at lulesh.cc:233
> 1.2 y 0x0000000000409c0c in
> CalcKinematicsForElems(Domain&, double, int)
> at lulesh.cc:233
>
> And we find all these locations:
> Compilation Unit name: lulesh.cc
> [403eb0, ffffffffffffffff) /g/g90/devkota1/LULESH/lulesh.cc:233
> [405477, ffffffffffffffff) /g/g90/devkota1/LULESH/lulesh.h:233
> [4060a0, ffffffffffffffff) /g/g90/devkota1/LULESH/lulesh.cc:233
> [409c0c, ffffffffffffffff) /g/g90/devkota1/LULESH/lulesh.cc:233
>
> But we need to get the whole range, lower and upper addresses.
Is this in gdb? Or do you mean using one of the elfutils tools or
libraries?
To see how addresses map to source code lines using eu-readelf, try
eu-readelf --debug-dump=line and --debug-dump=decodedline
When using the libdw interface you are probably looking for
dwarf_next_lines () and dwarf_linesrc (), you can then use the
different dwarf_line* () functions to get at the attributes.
Cheers,
Mark
