[Crash-utility] Re: [PATCH] gdb: fix the "p" command incorrectly print the value of a global variable

Date: Wed, 6 Mar 2024 14:31:27 +0800 From: Lianbo Jiang&lt;lijiang(a)redhat.com&gt; Subject: [Crash-utility] [PATCH] gdb: fix the "p" command incorrectly print the value of a global variable To:devel@lists.crash-utility.osci.io Message-ID:<20240306063127.477337-1-lijiang@redhat.com> Content-Type: text/plain; charset="US-ASCII"; x-default=true Some objects format may potentially support copy relocations, but currently the maybe_copied is always initialized to 0 in the symbol(). And the type is 'mst_file_bss', not always the 'mst_bss' or 'mst_data' in the lookup_minimal_symbol_linkage(). For example: (gdb) p *msymbol $42 = {<general_symbol_info> = {m_name = 0x349812f "test_no_static", value = {ivalue = 8, block = 0x8, bytes = 0x8 <error: Cannot access memory at address 0x8>, address = 8, common_block = 0x8, chain = 0x8}, language_specific = { obstack = 0x0, demangled_name = 0x0}, m_language = language_auto, ada_mangled = 0, section = 20}, size = 4, filename = 0x6db3440 "test_sanity.c", type = mst_file_bss, created_by_gdb = 0, target_flag_1 = 0, target_flag_2 = 0, has_size = 1, maybe_copied = 0, name_set = 1, hash_next = 0x0, demangled_hash_next = 0x0} This causes a problem that the 'p' command can not work well as expected, and always gets an error: crash> mod -s test_sanity /home/test_sanity.ko MODULE NAME BASE SIZE OBJECT FILE ffffffffc1084040 test_sanity ffffffffc1082000 16384 /home/test_sanity.ko crash> p test_no_static p: gdb request failed: p test_no_static crash> With the patch: crash> mod -s test_sanity /home/test_sanity.ko MODULE NAME BASE SIZE OBJECT FILE ffffffffc1084040 test_sanity ffffffffc1082000 16384 /home/test_sanity.ko crash> p test_no_static test_no_static = $1 = 5 crash> Signed-off-by: Lianbo Jiang&lt;lijiang(a)redhat.com&gt; --- Here is the test case: #include <linux/kernel.h> #include <linux/module.h> int test_no = 0; static int test_no_static = 0; static int test_init(void) { test_no += 5; test_no_static += 5; printk(KERN_INFO "%d static=%d\n", test_no, test_no_static); return 0; } static void test_exit(void) { test_no += 7; test_no_static += 7; printk(KERN_INFO "%d static=%d\n", test_no, test_no_static); } module_init(test_init); module_exit(test_exit); MODULE_LICENSE("GPL"); gdb-10.2.patch | 24 ++++++++++++++++++++++++ 1 file changed, 24 insertions(+) diff --git a/gdb-10.2.patch b/gdb-10.2.patch index a7018a249118..35388ba03e25 100644 --- a/gdb-10.2.patch +++ b/gdb-10.2.patch @@ -16057,3 +16057,27 @@ exit 0 m10200-dis.c m10200-opc.c m10300-dis.c +--- gdb-10.2/gdb/minsyms.c.orig ++++ gdb-10.2/gdb/minsyms.c +@@ -535,7 +535,9 @@ lookup_minimal_symbol_linkage (const char *name, struct objfile *objf) + { + if (strcmp (msymbol->linkage_name (), name) == 0 + && (MSYMBOL_TYPE (msymbol) == mst_data +- || MSYMBOL_TYPE (msymbol) == mst_bss)) ++ || MSYMBOL_TYPE (msymbol) == mst_bss ++ || MSYMBOL_TYPE (msymbol) == mst_file_bss ++ || MSYMBOL_TYPE (msymbol) == mst_file_data)) + return {msymbol, objfile}; + } + } +--- gdb-10.2/gdb/symtab.h.orig ++++ gdb-10.2/gdb/symtab.h +@@ -1110,7 +1110,7 @@ struct symbol : public general_symbol_info, public allocate_on_obstack + is_objfile_owned (1), + is_argument (0), + is_inlined (0), +- maybe_copied (0), ++ maybe_copied (1),/* The objfile potentially supports copy relocations. */ + subclass (SYMBOL_NONE) + { + /* We can't use an initializer list for members of a base class, and -- 2.41.0