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?
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?
> int
> dwarf_cu_dwp_section_info (Dwarf_CU *cu, unsigned int section,
> Dwarf_Off *offsetp, Dwarf_Off *sizep)
> diff --git a/libdw/dwarf_end.c b/libdw/dwarf_end.c
> index b7f817d9..78224ddb 100644
> --- a/libdw/dwarf_end.c
> +++ b/libdw/dwarf_end.c
> @@ -66,7 +66,9 @@ cu_free (void *arg)
> /* The fake_addr_cu might be shared, only release one. */
> if (p->dbg->fake_addr_cu == p->split->dbg->fake_addr_cu)
> p->split->dbg->fake_addr_cu = NULL;
> - INTUSE(dwarf_end) (p->split->dbg);
> + /* There is only one DWP file. We free it later. */
> + if (p->split->dbg != p->dbg->dwp_dwarf)
> + INTUSE(dwarf_end) (p->split->dbg);
> }
> }
> }
> @@ -147,6 +149,12 @@ dwarf_end (Dwarf *dwarf)
> close (dwarf->alt_fd);
> }
>
> + if (dwarf->dwp_fd != -1)
> + {
> + INTUSE(dwarf_end) (dwarf->dwp_dwarf);
> + close (dwarf->dwp_fd);
> + }
> +
> /* The cached path and dir we found the Dwarf ELF file in. */
> free (dwarf->elfpath);
> free (dwarf->debugdir);
OK
> diff --git a/libdw/libdwP.h b/libdw/libdwP.h
> index 214d1711..16355274 100644
> --- a/libdw/libdwP.h
> +++ b/libdw/libdwP.h
> @@ -180,6 +180,9 @@ struct Dwarf
> /* dwz alternate DWARF file. */
> Dwarf *alt_dwarf;
>
> + /* DWARF package file. */
> + Dwarf *dwp_dwarf;
> +
> /* The section data. */
> Elf_Data *sectiondata[IDX_last];
>
> @@ -197,6 +200,9 @@ struct Dwarf
> close this file descriptor. */
> int alt_fd;
>
> + /* File descriptor of DWARF package file. */
> + int dwp_fd;
> +
> /* Information for traversing the .debug_pubnames section. This is
> an array and separately allocated with malloc. */
> struct pubnames_s
> @@ -719,6 +725,10 @@ extern int __libdw_dwp_find_unit (Dwarf *dbg, bool
> debug_types, Dwarf_Off off,
> Dwarf_Off *abbrev_offsetp)
> __nonnull_attribute__ (1, 7, 8) internal_function;
>
> +/* Find the compilation unit in a DWARF package file with the given id. */
> +extern Dwarf_CU *__libdw_dwp_findcu_id (Dwarf *dbg, uint64_t unit_id8)
> + __nonnull_attribute__ (1) internal_function;
> +
> /* Get abbreviation with given code. */
> extern Dwarf_Abbrev *__libdw_findabbrev (struct Dwarf_CU *cu,
> unsigned int code)
OK.
> @@ -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?
> 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.
> + memcpy (dwp_path, cu->dbg->elfpath, elfpath_len);
> + strcpy (dwp_path + elfpath_len, ".dwp");
> + int dwp_fd = open (dwp_path, O_RDONLY);
> + free (dwp_path);
> + if (dwp_fd != -1)
> + {
> + Dwarf *dwp_dwarf = dwarf_begin (dwp_fd, DWARF_C_READ);
> + /* There's no way to know whether we got the correct file until
> + we look up the unit, but it should at least be a dwp file. */
> + if (dwp_dwarf != NULL
> + && (dwp_dwarf->sectiondata[IDX_debug_cu_index] != NULL
> + || dwp_dwarf->sectiondata[IDX_debug_tu_index] != NULL))
> + {
> + cu->dbg->dwp_dwarf = dwp_dwarf;
> + cu->dbg->dwp_fd = dwp_fd;
> + }
> + else
> + close (dwp_fd);
> + }
> + }
> + if (cu->dbg->dwp_dwarf == NULL)
> + cu->dbg->dwp_dwarf = (Dwarf *) -1;
> + }
> +
> + if (cu->dbg->dwp_dwarf != (Dwarf *) -1)
> + {
> + Dwarf_CU *split = __libdw_dwp_findcu_id (cu->dbg->dwp_dwarf,
> + cu->unit_id8);
> + if (split != NULL)
> + {
> + if (tsearch (split->dbg, &cu->dbg->split_tree,
> + __libdw_finddbg_cb) == NULL)
> + {
> + /* Something went wrong. Don't link. */
> + __libdw_seterrno (DWARF_E_NOMEM);
> + return;
> + }
Same as above.
> + /* Link skeleton and split compile units. */
> + __libdw_link_skel_split (cu, split);
> + }
> + }
> +}
OK.
> Dwarf_CU *
> internal_function
> __libdw_find_split_unit (Dwarf_CU *cu)
> @@ -98,14 +159,18 @@ __libdw_find_split_unit (Dwarf_CU *cu)
> same id as the skeleton. */
> if (cu->unit_type == DW_UT_skeleton)
> {
> + /* First, try the dwp file. */
> + try_dwp_file (cu);
> +
> Dwarf_Die cudie = CUDIE (cu);
> Dwarf_Attribute dwo_name;
> - /* It is fine if dwo_dir doesn't exists, but then dwo_name needs
> - to be an absolute path. */
> - if (dwarf_attr (&cudie, DW_AT_dwo_name, &dwo_name) != NULL
> - || dwarf_attr (&cudie, DW_AT_GNU_dwo_name, &dwo_name) != NULL)
> + /* Try a dwo file. It is fine if dwo_dir doesn't exist, but then
> + dwo_name needs to be an absolute path. */
> + if (cu->split == (Dwarf_CU *) -1
> + && (dwarf_attr (&cudie, DW_AT_dwo_name, &dwo_name) != NULL
> + || dwarf_attr (&cudie, DW_AT_GNU_dwo_name, &dwo_name) != NULL))
> {
> - /* First try the dwo file name in the same directory
> + /* Try the dwo file name in the same directory
> as we found the skeleton file. */
> const char *dwo_file = dwarf_formstring (&dwo_name);
> const char *debugdir = cu->dbg->debugdir;
OK. Because try_dwp_file will call __libdw_link_skel_split to set
cu->split.
This again will have to be analyzed carefully when we add the
thread-safety work.
Thanks,
Mark
