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

Hi Lianbo, On Wed, Mar 6, 2024 at 2:32 PM Lianbo Jiang <lijiang(a)redhat.com&gt; wrote: > > 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} > The whole bug is around test_no_static, which is a static variable in the ko. However the added code to lookup_minimal_symbol_linkage() is mst_file_bss/mst_file_data. So I guess test_no_static's symbol type

"test_no_static" instead of "test_sanity.c" for "p *msymbol", so it can be clearer for the adding of mst_file_bss/mst_file_data. Personally I think the symbol "test_sanity.c" doesn't make sense here.

Tao Liu > 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 = $1 = 5 > crash> > > Signed-off-by: Lianbo Jiang <lijiang(a)redhat.com&gt; > --- > Here is the test case: > #include <linux/kernel.h> > #include <linux/module.h> > > int test_no = 0; > static int test_no_static = 0; > > static int test_init(void) > { > test_no += 5; > test_no_static += 5; > printk(KERN_INFO "%d static=%d\n", test_no, test_no_static); > return 0; > } > static void test_exit(void) > > { > test_no += 7; > test_no_static += 7; > printk(KERN_INFO "%d static=%d\n", test_no, test_no_static); > } > module_init(test_init); > module_exit(test_exit); > MODULE_LICENSE("GPL"); > > > gdb-10.2.patch | 24 ++++++++++++++++++++++++ > 1 file changed, 24 insertions(+) > > diff --git a/gdb-10.2.patch b/gdb-10.2.patch > index a7018a249118..35388ba03e25 100644 > --- a/gdb-10.2.patch > +++ b/gdb-10.2.patch > @@ -16057,3 +16057,27 @@ exit 0 > m10200-dis.c > m10200-opc.c > m10300-dis.c > +--- gdb-10.2/gdb/minsyms.c.orig > ++++ gdb-10.2/gdb/minsyms.c > +@@ -535,7 +535,9 @@ lookup_minimal_symbol_linkage (const char *name, struct objfile *objf) > + { > + if (strcmp (msymbol->linkage_name (), name) == 0 > + && (MSYMBOL_TYPE (msymbol) == mst_data > +- || MSYMBOL_TYPE (msymbol) == mst_bss)) > ++ || MSYMBOL_TYPE (msymbol) == mst_bss > ++ || MSYMBOL_TYPE (msymbol) == mst_file_bss > ++ || MSYMBOL_TYPE (msymbol) == mst_file_data)) > + return {msymbol, objfile}; > + } > + } > +--- gdb-10.2/gdb/symtab.h.orig > ++++ gdb-10.2/gdb/symtab.h > +@@ -1110,7 +1110,7 @@ struct symbol : public general_symbol_info, public allocate_on_obstack > + is_objfile_owned (1), > + is_argument (0), > + is_inlined (0), > +- maybe_copied (0), > ++ maybe_copied (1),/* The objfile potentially supports copy relocations. */ > + subclass (SYMBOL_NONE) > + { > + /* We can't use an initializer list for members of a base class, and > -- > 2.41.0 > -- > Crash-utility mailing list -- devel(a)lists.crash-utility.osci.io > To unsubscribe send an email to devel-leave(a)lists.crash-utility.osci.io > https://${domain_name}/admin/lists/devel.lists.crash-utility.osci.io/ > Contribution Guidelines: https://github.com/crash-utility/crash/wiki