From 973695d6bb824a1e724d5ea24e7ece013109dc74 Mon Sep 17 00:00:00 2001 From: Kevin Buettner Date: Fri, 7 Aug 2020 13:07:44 -0700 Subject: [PATCH] Work around incorrect/broken pathnames in NT_FILE note Luis Machado reported some regressions after I pushed recent core file related patches fixing BZ 25631: FAIL: gdb.base/corefile.exp: backtrace in corefile.exp FAIL: gdb.base/corefile.exp: core-file warning-free FAIL: gdb.base/corefile.exp: print func2::coremaker_local FAIL: gdb.base/corefile.exp: up in corefile.exp FAIL: gdb.base/corefile.exp: up in corefile.exp (reinit) This commit fixes these regressions. Thanks to Luis for testing an earlier version of the patch. (I was unable to reproduce these regressions in various test environments that I created.) Luis is testing in a docker container which is using the AUFS storage driver. It turns out that the kernel is placing docker host paths in the NT_FILE note instead of paths within the container. I've made a similar docker environment (though apparently not similar enough to reproduce the regressions). This is one of the paths that I see mentioned in the warning messages printed while loading the core file during NT_FILE note processing - note that I've shortened the path component starting with "d07c4": /var/lib/docker/aufs/diff/d07c4...21/lib/x86_64-linux-gnu/ld-2.27.so This is a path on the docker host; it does not exist in the container. In the docker container, this is the path: /lib/x86_64-linux-gnu/ld-2.27.so My first thought was to disable all NT_FILE mappings when any path was found to be bad. This would have caused GDB to fall back to accessing memory using the file stratum as it did before I added the NT_FILE note loading code. After further consideration, I realized that we could do better than this. For file-backed memory access, we can still use the NT_FILE mappings when available, and then attempt to access memory using the file stratum constrained to those address ranges corresponding to the "broken" mappings. In order to test it, I made some additions to corefile2.exp in which the test case's executable is renamed. The core file is then loaded; due to the fact that the executable has been renamed, those mappings will be unavailable. After loading the core file, the executable is renamed back to its original name at which point it is loaded using GDB's "file" command. The "interesting" tests are then run. These tests will print out values in file-backed memory regions along with mmap'd regions placed within/over the file-backed regions. Despite the fact that the executable could not be found during the NT_FILE note processing, these tests still work correctly due to the fact that memory is available from the file stratum combined with the fact that the broken NT_FILE mappings are used to prevent file-backed access outside of the "broken" mappings. gdb/ChangeLog: * corelow.c (unordered_set): Include. (class core_target): Add field 'm_core_unavailable_mappings'. (core_target::build_file_mappings): Print only one warning per inaccessible file. Add unavailable/broken mappings to m_core_unavailable_mappings. (core_target::xfer_partial): Call... (core_target::xfer_memory_via_mappings): New method. gdb/testsuite/ChangeLog: * gdb.base/corefile2.exp (renamed binfile): New tests. --- gdb/ChangeLog | 10 ++++ gdb/corelow.c | 84 +++++++++++++++++++++++++--- gdb/testsuite/ChangeLog | 4 ++ gdb/testsuite/gdb.base/corefile2.exp | 27 +++++++++ 4 files changed, 117 insertions(+), 8 deletions(-) diff --git a/gdb/ChangeLog b/gdb/ChangeLog index 7aadd870423..4840de8591a 100644 --- a/gdb/ChangeLog +++ b/gdb/ChangeLog @@ -1,3 +1,13 @@ +2020-08-31 Kevin Buettner + + * corelow.c (unordered_set): Include. + (class core_target): Add field 'm_core_unavailable_mappings'. + (core_target::build_file_mappings): Print only one warning + per inaccessible file. Add unavailable/broken mappings + to m_core_unavailable_mappings. + (core_target::xfer_partial): Call... + (core_target::xfer_memory_via_mappings): New method. + 2020-08-31 Simon Marchi * dwarf2/read.c (struct field_info) : Change diff --git a/gdb/corelow.c b/gdb/corelow.c index b6ee219f57c..96ec739c62f 100644 --- a/gdb/corelow.c +++ b/gdb/corelow.c @@ -47,6 +47,7 @@ #include "build-id.h" #include "gdbsupport/pathstuff.h" #include +#include #include "gdbcmd.h" #ifndef O_LARGEFILE @@ -131,9 +132,21 @@ private: /* per-core data */ information about memory mapped files. */ target_section_table m_core_file_mappings {}; + /* Unavailable mappings. These correspond to pathnames which either + weren't found or could not be opened. Knowing these addresses can + still be useful. */ + std::vector m_core_unavailable_mappings; + /* Build m_core_file_mappings. Called from the constructor. */ void build_file_mappings (); + /* Helper method for xfer_partial. */ + enum target_xfer_status xfer_memory_via_mappings (gdb_byte *readbuf, + const gdb_byte *writebuf, + ULONGEST offset, + ULONGEST len, + ULONGEST *xfered_len); + /* FIXME: kettenis/20031023: Eventually this field should disappear. */ struct gdbarch *m_core_gdbarch = NULL; @@ -182,6 +195,7 @@ void core_target::build_file_mappings () { std::unordered_map bfd_map; + std::unordered_set unavailable_paths; /* See linux_read_core_file_mappings() in linux-tdep.c for an example read_core_file_mappings method. */ @@ -216,9 +230,12 @@ core_target::build_file_mappings () = exec_file_find (filename, NULL); if (expanded_fname == nullptr) { - warning (_("Can't open file %s during file-backed mapping " - "note processing"), - filename); + m_core_unavailable_mappings.emplace_back (start, end - start); + /* Print just one warning per path. */ + if (unavailable_paths.insert (filename).second) + warning (_("Can't open file %s during file-backed mapping " + "note processing"), + filename); return; } @@ -227,6 +244,7 @@ core_target::build_file_mappings () if (bfd == nullptr || !bfd_check_format (bfd, bfd_object)) { + m_core_unavailable_mappings.emplace_back (start, end - start); /* If we get here, there's a good chance that it's due to an internal error. We issue a warning instead of an internal error because of the possibility that the @@ -268,6 +286,8 @@ core_target::build_file_mappings () ts->owner = nullptr; ts->the_bfd_section = sec; }); + + normalize_mem_ranges (&m_core_unavailable_mappings); } static void add_to_thread_list (bfd *, asection *, void *); @@ -728,6 +748,57 @@ core_target::files_info () print_section_info (&m_core_section_table, core_bfd); } +/* Helper method for core_target::xfer_partial. */ + +enum target_xfer_status +core_target::xfer_memory_via_mappings (gdb_byte *readbuf, + const gdb_byte *writebuf, + ULONGEST offset, ULONGEST len, + ULONGEST *xfered_len) +{ + enum target_xfer_status xfer_status; + + xfer_status = (section_table_xfer_memory_partial + (readbuf, writebuf, + offset, len, xfered_len, + m_core_file_mappings.sections, + m_core_file_mappings.sections_end)); + + if (xfer_status == TARGET_XFER_OK || m_core_unavailable_mappings.empty ()) + return xfer_status; + + /* There are instances - e.g. when debugging within a docker + container using the AUFS storage driver - where the pathnames + obtained from the note section are incorrect. Despite the path + being wrong, just knowing the start and end addresses of the + mappings is still useful; we can attempt an access of the file + stratum constrained to the address ranges corresponding to the + unavailable mappings. */ + + ULONGEST memaddr = offset; + ULONGEST memend = offset + len; + + for (const auto &mr : m_core_unavailable_mappings) + { + if (address_in_mem_range (memaddr, &mr)) + { + if (!address_in_mem_range (memend, &mr)) + len = mr.start + mr.length - memaddr; + + xfer_status = this->beneath ()->xfer_partial (TARGET_OBJECT_MEMORY, + NULL, + readbuf, + writebuf, + offset, + len, + xfered_len); + break; + } + } + + return xfer_status; +} + enum target_xfer_status core_target::xfer_partial (enum target_object object, const char *annex, gdb_byte *readbuf, const gdb_byte *writebuf, @@ -761,11 +832,8 @@ core_target::xfer_partial (enum target_object object, const char *annex, result. If not, check the stratum beneath us, which should be the file stratum. */ if (m_core_file_mappings.sections != nullptr) - xfer_status = section_table_xfer_memory_partial - (readbuf, writebuf, - offset, len, xfered_len, - m_core_file_mappings.sections, - m_core_file_mappings.sections_end); + xfer_status = xfer_memory_via_mappings (readbuf, writebuf, offset, + len, xfered_len); else xfer_status = this->beneath ()->xfer_partial (object, annex, readbuf, writebuf, offset, len, diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog index 148f31d26dd..e50b2352d9f 100644 --- a/gdb/testsuite/ChangeLog +++ b/gdb/testsuite/ChangeLog @@ -1,3 +1,7 @@ +2020-08-31 Kevin Buettner + + * gdb.base/corefile2.exp (renamed binfile): New tests. + 2020-08-31 Simon Marchi * gdb.dwarf2/dw2-reg-undefined.exp: Remove spurious #. diff --git a/gdb/testsuite/gdb.base/corefile2.exp b/gdb/testsuite/gdb.base/corefile2.exp index 5de7ead4d44..38b8eb770bd 100644 --- a/gdb/testsuite/gdb.base/corefile2.exp +++ b/gdb/testsuite/gdb.base/corefile2.exp @@ -143,6 +143,33 @@ gdb_test_multiple $test "" { } } +# Test again with executable renamed during loading of core file. + +with_test_prefix "renamed binfile" { + # Don't load $binfile in this call to clean_restart. (BFD will + # complain that $binfile has disappeared after the rename if it's + # loaded first.) + clean_restart + + # Rename $binfile so that it won't be found during loading of + # the core file. + set hide_binfile [standard_output_file "${testfile}.hide"] + remote_exec host "mv -f $binfile $hide_binfile" + + # Load core file - check that a warning is printed. + global xfail + if { $xfail } { setup_xfail "*-*-*" } + gdb_test "core-file $corefile" \ + "warning: Can't open file.*during.* note processing.*Core was generated by .*\#0 .*\(\)" \ + "load core file without having first loaded binfile" + + # Restore $binfile and then load it. + remote_exec host "mv -f $hide_binfile $binfile" + gdb_load ${binfile} + + do_tests +} + # Restart and run to the abort call. clean_restart $binfile -- 2.30.2