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Add support for GCC dwarf2 data #13

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Add support for GCC dwarf2 data #13

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jwadams
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@jwadams jwadams commented Sep 21, 2019

libdrgn/dwarf_info_cache.c uses dwarf_formudata() to pull constants
(like structure member offsets) out of the dwarf data. Unfortunately,
GCC in -gdwarf-2 mode generates structure constants as blocks with
a single "DW_OP_plus_uconst" operation, which doesn't work with
dwarf_formudata().

This patch introduces a drgn_formudata() wrapper around
dwarf_formudata(), which upon failure sees if the attribute is a
block of that form, and if so returns the proper value. We have all
the existing dwarf_formudata() callsites use the new wrapper. This
allows for debugging kernels with dwarf-2 data (which is the default
for x86 linux)

@jwadams
Add support for GCC dwarf2 data
de8492d 
libdrgn/dwarf_info_cache.c uses dwarf_formudata() to pull constants
(like structure member offsets) out of the dwarf data.  Unfortunately,
GCC in -gdwarf-2 mode generates structure constants as blocks with
a single "DW_OP_plus_uconst" operation, which doesn't work with
dwarf_formudata().

This patch introduces a drgn_formudata() wrapper around
dwarf_formudata(), which upon failure sees if the attribute is a
block of that form, and if so returns the proper value.  We have all
the existing dwarf_formudata() callsites use the new wrapper.  This
allows for debugging kernels with dwarf-2 data (which is the default
for x86 linux)
osandov
osandov requested changes Sep 26, 2019
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Thanks for the fix!

libdrgn/dwarf_info_cache.c
return (0);
}
/* Try for the dwarf2 case, bailing out if anything looks odd */
if (dwarf_formblock(attr, &block) == 0) {
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Can we use dwarf_getlocation()? See drgn_object_from_dwarf_variable() for an example.

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We could; my only worry is the overhead of the memory allocation (internal to libdw, which caches them, presumably forever) for each every structure member we ever see. It looks like it would work, though. If you're not worried about that overhead, it would certainly make this function simpler.

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Yeah let's do the simpler way for now. If it ends up causing issues, we can bring back your optimized version.

libdrgn/dwarf_info_cache.c Show resolved Hide resolved
osandov added a commit that referenced this pull request May 6, 2021
@osandov
CI: temporarily disable Clang
1cc3868 
Clang tests are hitting this assertion in libomp (libomp5-10
1:10.0.0-4ubuntu1):

  Assertion failure at kmp_tasking.cpp(501): taskdata->td_flags.tasktype == 1.
  OMP: Error #13: Assertion failure at kmp_tasking.cpp(501).
  OMP: Hint Please submit a bug report with this message, compile and run commands used, and machine configuration info including native compiler and operating system versions. Faster response will be obtained by including all program sources. For information on submitting this issue, please see https://bugs.llvm.org/.

Disable Clang builds until we figure out what's going on.

Signed-off-by: Omar Sandoval <osandov@osandov.com>
@osandov osandov closed this in 8b4532c Aug 16, 2021
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osandov commented Aug 16, 2021

I ran into this again recently, so I finally got around to applying your approach with some updates. (Belated) thanks!

kylee0215 added a commit to kylee0215/drgn that referenced this pull request Sep 4, 2024
@kylee0215
contrib: add script to dump page_owner info
dfa8d9f 
Sample output:

Page allocated via order 0, gfp_mask: 0x140cca, pid: 74, tgid: 74 (b'kworker/u32:2'), ts 1189257596 ns, free_ts 0 ns
PFN: 262203, Flags: 0x3fffe000004003c
#0  set_page_owner (./include/linux/page_owner.h:32:3)
osandov#1  post_alloc_hook (mm/page_alloc.c:1502:2)
osandov#2  prep_new_page (mm/page_alloc.c:1510:2)
osandov#3  get_page_from_freelist (mm/page_alloc.c:3489:4)
osandov#4  __alloc_pages_noprof (mm/page_alloc.c:4747:9)
osandov#5  alloc_pages_mpol_noprof (mm/mempolicy.c:2263:9)
osandov#6  folio_alloc_mpol_noprof (mm/mempolicy.c:2281:9)
osandov#7  shmem_alloc_folio (mm/shmem.c:1726:10)
osandov#8  shmem_alloc_and_add_folio (mm/shmem.c:1786:11)
osandov#9  shmem_get_folio_gfp (mm/shmem.c:2192:10)
osandov#10 shmem_get_folio (mm/shmem.c:2297:9)
osandov#11 shmem_write_begin (mm/shmem.c:2902:8)
osandov#12 generic_perform_write (mm/filemap.c:4019:12)
osandov#13 shmem_file_write_iter (mm/shmem.c:3078:8)
osandov#14 __kernel_write_iter (fs/read_write.c:523:8)
osandov#15 __kernel_write (fs/read_write.c:543:9)
osandov#16 kernel_write (fs/read_write.c:564:9)
osandov#17 kernel_write (fs/read_write.c:554:9)
osandov#18 xwrite (init/initramfs.c:33:16)
osandov#19 do_copy (init/initramfs.c:405:7)
osandov#20 write_buffer (init/initramfs.c:452:10)
osandov#21 unpack_to_rootfs (init/initramfs.c:505:14)
...

Signed-off-by: Kuan-Ying Lee <kuan-ying.lee@canonical.com>
kylee0215 added a commit to kylee0215/drgn that referenced this pull request Sep 4, 2024
@kylee0215
contrib: add script to dump page_owner info
b5c4458 
python3 -m drgn -s ./vmlinux -c ./vmcore contrib/page_owner.py --pfn 262144

Sample output:

Page last allocated via order 0, gfp_mask: 0x140cca, pid: 74, tgid: 74 (kworker/u32:2), ts 1189257596 ns, free_ts 0 ns
PFN: 262203, Flags: 0x3fffe000004003c
#0  set_page_owner (./include/linux/page_owner.h:32:3)
osandov#1  post_alloc_hook (mm/page_alloc.c:1502:2)
osandov#2  prep_new_page (mm/page_alloc.c:1510:2)
osandov#3  get_page_from_freelist (mm/page_alloc.c:3489:4)
osandov#4  __alloc_pages_noprof (mm/page_alloc.c:4747:9)
osandov#5  alloc_pages_mpol_noprof (mm/mempolicy.c:2263:9)
osandov#6  folio_alloc_mpol_noprof (mm/mempolicy.c:2281:9)
osandov#7  shmem_alloc_folio (mm/shmem.c:1726:10)
osandov#8  shmem_alloc_and_add_folio (mm/shmem.c:1786:11)
osandov#9  shmem_get_folio_gfp (mm/shmem.c:2192:10)
osandov#10 shmem_get_folio (mm/shmem.c:2297:9)
osandov#11 shmem_write_begin (mm/shmem.c:2902:8)
osandov#12 generic_perform_write (mm/filemap.c:4019:12)
osandov#13 shmem_file_write_iter (mm/shmem.c:3078:8)
osandov#14 __kernel_write_iter (fs/read_write.c:523:8)
osandov#15 __kernel_write (fs/read_write.c:543:9)
osandov#16 kernel_write (fs/read_write.c:564:9)
osandov#17 kernel_write (fs/read_write.c:554:9)
osandov#18 xwrite (init/initramfs.c:33:16)
osandov#19 do_copy (init/initramfs.c:405:7)
osandov#20 write_buffer (init/initramfs.c:452:10)
osandov#21 unpack_to_rootfs (init/initramfs.c:505:14)
...

Signed-off-by: Kuan-Ying Lee <kuan-ying.lee@canonical.com>
kylee0215 added a commit to kylee0215/drgn that referenced this pull request Sep 4, 2024
@kylee0215
contrib: add script to dump page_owner info
ae95d0a 
python3 -m drgn -s ./vmlinux -c ./vmcore contrib/page_owner.py --pfn 262144

Sample output:

page_owner tracks the page as allocated
Page last allocated via order 0, gfp_mask: 0x140cca, pid: 74, tgid: 74 (kworker/u32:2), ts 1187644920 ns, free_ts 0 ns
PFN: 262144, Flags: 0x3fffe000004003c
#0  set_page_owner (./include/linux/page_owner.h:32:3)
osandov#1  post_alloc_hook (mm/page_alloc.c:1502:2)
osandov#2  prep_new_page (mm/page_alloc.c:1510:2)
osandov#3  get_page_from_freelist (mm/page_alloc.c:3489:4)
osandov#4  __alloc_pages_noprof (mm/page_alloc.c:4747:9)
osandov#5  alloc_pages_mpol_noprof (mm/mempolicy.c:2263:9)
osandov#6  folio_alloc_mpol_noprof (mm/mempolicy.c:2281:9)
osandov#7  shmem_alloc_folio (mm/shmem.c:1726:10)
osandov#8  shmem_alloc_and_add_folio (mm/shmem.c:1786:11)
osandov#9  shmem_get_folio_gfp (mm/shmem.c:2192:10)
osandov#10 shmem_get_folio (mm/shmem.c:2297:9)
osandov#11 shmem_write_begin (mm/shmem.c:2902:8)
osandov#12 generic_perform_write (mm/filemap.c:4019:12)
osandov#13 shmem_file_write_iter (mm/shmem.c:3078:8)
osandov#14 __kernel_write_iter (fs/read_write.c:523:8)
osandov#15 __kernel_write (fs/read_write.c:543:9)
osandov#16 kernel_write (fs/read_write.c:564:9)
osandov#17 kernel_write (fs/read_write.c:554:9)
osandov#18 xwrite (init/initramfs.c:33:16)
osandov#19 do_copy (init/initramfs.c:405:7)
osandov#20 write_buffer (init/initramfs.c:452:10)
osandov#21 unpack_to_rootfs (init/initramfs.c:505:14)
page_owner free stack trace missing
...

Signed-off-by: Kuan-Ying Lee <kuan-ying.lee@canonical.com>
kylee0215 added a commit to kylee0215/drgn that referenced this pull request Sep 4, 2024
@kylee0215
contrib: add script to dump page_owner information
f91b0c6 
python3 -m drgn -s ./vmlinux -c ./vmcore contrib/page_owner.py --pfn 262144

Sample output:

page_owner tracks the page as allocated
Page last allocated via order 0, gfp_mask: 0x140cca, pid: 74, tgid: 74 (kworker/u32:2), ts 1187644920 ns, free_ts 0 ns
PFN: 262144, Flags: 0x3fffe000004003c
#0  set_page_owner (./include/linux/page_owner.h:32:3)
osandov#1  post_alloc_hook (mm/page_alloc.c:1502:2)
osandov#2  prep_new_page (mm/page_alloc.c:1510:2)
osandov#3  get_page_from_freelist (mm/page_alloc.c:3489:4)
osandov#4  __alloc_pages_noprof (mm/page_alloc.c:4747:9)
osandov#5  alloc_pages_mpol_noprof (mm/mempolicy.c:2263:9)
osandov#6  folio_alloc_mpol_noprof (mm/mempolicy.c:2281:9)
osandov#7  shmem_alloc_folio (mm/shmem.c:1726:10)
osandov#8  shmem_alloc_and_add_folio (mm/shmem.c:1786:11)
osandov#9  shmem_get_folio_gfp (mm/shmem.c:2192:10)
osandov#10 shmem_get_folio (mm/shmem.c:2297:9)
osandov#11 shmem_write_begin (mm/shmem.c:2902:8)
osandov#12 generic_perform_write (mm/filemap.c:4019:12)
osandov#13 shmem_file_write_iter (mm/shmem.c:3078:8)
osandov#14 __kernel_write_iter (fs/read_write.c:523:8)
osandov#15 __kernel_write (fs/read_write.c:543:9)
osandov#16 kernel_write (fs/read_write.c:564:9)
osandov#17 kernel_write (fs/read_write.c:554:9)
osandov#18 xwrite (init/initramfs.c:33:16)
osandov#19 do_copy (init/initramfs.c:405:7)
osandov#20 write_buffer (init/initramfs.c:452:10)
osandov#21 unpack_to_rootfs (init/initramfs.c:505:14)
page_owner free stack trace missing
...

Signed-off-by: Kuan-Ying Lee <kuan-ying.lee@canonical.com>
kylee0215 added a commit to kylee0215/drgn that referenced this pull request Oct 29, 2024
@kylee0215
contrib: add script to dump page_owner information
4a3f7b2 
python3 -m drgn -s ./vmlinux -c ./vmcore contrib/page_owner.py --pfn 262144

Sample output:

page_owner tracks the page as allocated
Page last allocated via order 0, gfp_mask: 0x140cca, pid: 74, tgid: 74 (kworker/u32:2), ts 1187644920 ns, free_ts 0 ns
PFN: 262144, Flags: 0x3fffe000004003c
#0  set_page_owner (./include/linux/page_owner.h:32:3)
osandov#1  post_alloc_hook (mm/page_alloc.c:1502:2)
osandov#2  prep_new_page (mm/page_alloc.c:1510:2)
osandov#3  get_page_from_freelist (mm/page_alloc.c:3489:4)
osandov#4  __alloc_pages_noprof (mm/page_alloc.c:4747:9)
osandov#5  alloc_pages_mpol_noprof (mm/mempolicy.c:2263:9)
osandov#6  folio_alloc_mpol_noprof (mm/mempolicy.c:2281:9)
osandov#7  shmem_alloc_folio (mm/shmem.c:1726:10)
osandov#8  shmem_alloc_and_add_folio (mm/shmem.c:1786:11)
osandov#9  shmem_get_folio_gfp (mm/shmem.c:2192:10)
osandov#10 shmem_get_folio (mm/shmem.c:2297:9)
osandov#11 shmem_write_begin (mm/shmem.c:2902:8)
osandov#12 generic_perform_write (mm/filemap.c:4019:12)
osandov#13 shmem_file_write_iter (mm/shmem.c:3078:8)
osandov#14 __kernel_write_iter (fs/read_write.c:523:8)
osandov#15 __kernel_write (fs/read_write.c:543:9)
osandov#16 kernel_write (fs/read_write.c:564:9)
osandov#17 kernel_write (fs/read_write.c:554:9)
osandov#18 xwrite (init/initramfs.c:33:16)
osandov#19 do_copy (init/initramfs.c:405:7)
osandov#20 write_buffer (init/initramfs.c:452:10)
osandov#21 unpack_to_rootfs (init/initramfs.c:505:14)
page_owner free stack trace missing
...

Signed-off-by: Kuan-Ying Lee <kuan-ying.lee@canonical.com>
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@jwadams @osandov