On Thu, Nov 02, 2023 at 08:56:14PM +0100, Mark Wielaard wrote:
> Hi Omar,
>
> On Wed, Sep 27, 2023 at 11:20:59AM -0700, Omar Sandoval wrote:
> > Try opening the file in the location suggested by the standard (the
> > skeleton file name + ".dwp") and looking up the unit in the package
> > index. The rest is similar to .dwo files, with slightly different
> > cleanup since a single Dwarf handle is shared.
>
> This seems a good default given it is what the standard says.
> But do you know of any distro doing this?
I don't. As far as I know, Meta and Google are the only ones using dwp
widely, and we're putting it in the location recommended by the
standard. (I think some Rust tooling is starting to pick dwp up, too,
but I haven't looked into it much.)
> The case I am wondering about is for separate .debug files (which
> surprisingly isn't standardized). In that case this would be
> foobar.debug.dwz (and not foobar.dwz).
>
> It might also be an idea to just create one file with both the
> skeletons and the .dwo and dwz index sections.
>
> > Signed-off-by: Omar Sandoval <osan...@fb.com>
> > ---
> > libdw/ChangeLog | 11 ++++-
> > libdw/dwarf_begin_elf.c | 1 +
> > libdw/dwarf_cu_dwp_section_info.c | 19 ++++++++
> > libdw/dwarf_end.c | 10 ++++-
> > libdw/libdwP.h | 16 ++++++-
> > libdw/libdw_find_split_unit.c | 75 ++++++++++++++++++++++++++++---
> > 6 files changed, 122 insertions(+), 10 deletions(-)
> >
> > diff --git a/libdw/ChangeLog b/libdw/ChangeLog
> > index f491587f..f37d9411 100644
> > --- a/libdw/ChangeLog
> > +++ b/libdw/ChangeLog
> > @@ -1,6 +1,8 @@
> > 2023-09-27 Omar Sandoval <osan...@fb.com>
> >
> > * libdw_find_split_unit.c (try_split_file): Make static.
> > + (try_dwp_file): New function.
> > + (__libdw_find_split_unit): Call try_dwp_file.
> > * dwarf_entrypc.c (dwarf_entrypc): Call dwarf_lowpc.
> > * dwarf_ranges.c (dwarf_ranges): Use skeleton ranges section for
> > skeleton units.
> > @@ -20,7 +22,8 @@
> > instead of dbg parameter, which is now unused.
> > * libdwP.h (Dwarf_Macro_Op_Table): Replace is_64bit with address_size
> > and offset_size. Add dbg.
> > - (Dwarf): Add cu_index and tu_index. Add elfpath.
> > + (Dwarf): Add cu_index and tu_index. Add elfpath. Add dwp_dwarf and
> > + dwp_fd.
> > (Dwarf_CU): Add dwp_row.
> > (Dwarf_Package_Index): New type.
> > (DW_SECT_TYPES): New macro.
> > @@ -31,6 +34,8 @@
> > (__libdw_debugdir): Replace declaration with...
> > (__libdw_elfpath): New declaration.
> > (__libdw_set_debugdir): New declaration.
> > + (__libdw_dwp_findcu_id): New declaration.
> > + (__libdw_link_skel_split): Handle .debug_addr for dwp.
> > * dwarf_begin_elf.c (dwarf_scnnames): Add IDX_debug_cu_index and
> > IDX_debug_tu_index.
> > (scn_to_string_section_idx): Ditto.
> > @@ -43,9 +48,11 @@
> > (__libdw_set_debugdir): New function.
> > (valid_p): Call __libdw_elfpath and __libdw_set_debugdir instead of
> > __libdw_debugdir.
> > + (dwarf_begin_elf): Initialize result->dwp_fd.
> > * Makefile.am (libdw_a_SOURCES): Add dwarf_cu_dwp_section_info.c.
> > * dwarf_end.c (dwarf_end): Free dwarf->cu_index and dwarf->tu_index.
> > - Free dwarf->elfpath.
> > + Free dwarf->elfpath. Free dwarf->dwp_dwarf and close dwarf->dwp_fd.
> > + (cu_free): Don't free split dbg if it is dwp_dwarf.
> > * dwarf_error.c (errmsgs): Add DWARF_E_UNKNOWN_SECTION.
> > * libdw.h (dwarf_cu_dwp_section_info): New declaration.
> > * libdw.map (ELFUTILS_0.190): Add dwarf_cu_dwp_section_info.
> > diff --git a/libdw/dwarf_begin_elf.c b/libdw/dwarf_begin_elf.c
> > index 323a91d0..ca2b7e2a 100644
> > --- a/libdw/dwarf_begin_elf.c
> > +++ b/libdw/dwarf_begin_elf.c
> > @@ -567,6 +567,7 @@ dwarf_begin_elf (Elf *elf, Dwarf_Cmd cmd, Elf_Scn
> > *scngrp)
> >
> > result->elf = elf;
> > result->alt_fd = -1;
> > + result->dwp_fd = -1;
> >
> > /* Initialize the memory handling. Initial blocks are allocated on first
> > actual allocation. */
> > diff --git a/libdw/dwarf_cu_dwp_section_info.c
> > b/libdw/dwarf_cu_dwp_section_info.c
> > index 6766fb9a..7bf08d9d 100644
> > --- a/libdw/dwarf_cu_dwp_section_info.c
> > +++ b/libdw/dwarf_cu_dwp_section_info.c
> > @@ -340,6 +340,25 @@ __libdw_dwp_find_unit (Dwarf *dbg, bool debug_types,
> > Dwarf_Off off,
> > abbrev_offsetp, NULL);
> > }
> >
> > +Dwarf_CU *
> > +internal_function
> > +__libdw_dwp_findcu_id (Dwarf *dbg, uint64_t unit_id8)
> > +{
> > + Dwarf_Package_Index *index = __libdw_package_index (dbg, false);
> > + uint32_t unit_row;
> > + Dwarf_Off offset;
> > + Dwarf_CU *cu;
> > + if (__libdw_dwp_unit_row (index, unit_id8, &unit_row) == 0
> > + && __libdw_dwp_section_info (index, unit_row, DW_SECT_INFO, &offset,
> > + NULL) == 0
> > + && (cu = __libdw_findcu (dbg, offset, false)) != NULL
> > + && cu->unit_type == DW_UT_split_compile
> > + && cu->unit_id8 == unit_id8)
> > + return cu;
> > + else
> > + return NULL;
> > +}
>
> No lookup for split_type?
Type units don't have a skeleton (except apparently in some early
prototypes of the DWARF4 GNU format), so there's no need to look them up
this way.
[snip]
> > @@ -1373,8 +1383,10 @@ __libdw_link_skel_split (Dwarf_CU *skel, Dwarf_CU
> > *split)
> > There is only one per split debug. */
> > Dwarf *dbg = skel->dbg;
> > Dwarf *sdbg = split->dbg;
> > - if (sdbg->sectiondata[IDX_debug_addr] == NULL
> > - && dbg->sectiondata[IDX_debug_addr] != NULL)
> > + if (dbg->sectiondata[IDX_debug_addr] != NULL
> > + && (sdbg->sectiondata[IDX_debug_addr] == NULL
> > + || (sdbg->sectiondata[IDX_debug_addr]
> > + == dbg->sectiondata[IDX_debug_addr])))
> > {
> > sdbg->sectiondata[IDX_debug_addr]
> > = dbg->sectiondata[IDX_debug_addr];
>
> ehe? What exactly are we checking here?
Oops, I could've sworn I added a comment here. A couple more lines of
context in the diff are helpful here:
@@ -1371,12 +1381,14 @@ __libdw_link_skel_split (Dwarf_CU *skel, Dwarf_CU
*split)
/* Get .debug_addr and addr_base greedy.
We also need it for the fake addr cu.
There is only one per split debug. */
Dwarf *dbg = skel->dbg;
Dwarf *sdbg = split->dbg;
- if (sdbg->sectiondata[IDX_debug_addr] == NULL
- && dbg->sectiondata[IDX_debug_addr] != NULL)
+ if (dbg->sectiondata[IDX_debug_addr] != NULL
+ && (sdbg->sectiondata[IDX_debug_addr] == NULL
+ || (sdbg->sectiondata[IDX_debug_addr]
+ == dbg->sectiondata[IDX_debug_addr])))
{
sdbg->sectiondata[IDX_debug_addr]
= dbg->sectiondata[IDX_debug_addr];
split->addr_base = __libdw_cu_addr_base (skel);
sdbg->fake_addr_cu = dbg->fake_addr_cu;
This is supposed to copy the .debug_addr section of the skeleton file to
the split file, and also copy the .debug_addr base of the skeleton unit
to the split unit. The former only needs to be done once per file, but
for DWP the latter needs to be done for every unit.
So the check is "link the .debug_addr info if this is the first time
we're linking this split file OR are we linking this split file to the
same skeleton file."
I'll add a comment.
> > diff --git a/libdw/libdw_find_split_unit.c b/libdw/libdw_find_split_unit.c
> > index 533f8072..e1e78951 100644
> > --- a/libdw/libdw_find_split_unit.c
> > +++ b/libdw/libdw_find_split_unit.c
> > @@ -85,6 +85,67 @@ try_split_file (Dwarf_CU *cu, const char *dwo_path)
> > }
> > }
> >
> > +static void
> > +try_dwp_file (Dwarf_CU *cu)
> > +{
> > + if (cu->dbg->dwp_dwarf == NULL)
> > + {
> > + if (cu->dbg->elfpath != NULL)
> > + {
> > + /* The DWARF 5 standard says "the package file is typically placed in
> > + the same directory as the application, and is given the same name
> > + with a '.dwp' extension". */
> > + size_t elfpath_len = strlen (cu->dbg->elfpath);
> > + char *dwp_path = malloc (elfpath_len + 5);
> > + if (dwp_path == NULL)
> > + {
> > + __libdw_seterrno (DWARF_E_NOMEM);
> > + return;
> > + }
>
> Yes, but the caller doesn't check for errors. So the seterrno is not
> very useful.
I think I copied that from try_split_file. Should I update the caller?
[snip]
Thanks!
