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

Hi, Tao Thanks for the comments. On Wed, Apr 3, 2024 at 11:45 AM Tao Liu <ltao(a)redhat.com&gt; wrote: > > 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 Just to be safe I added the type 'mst_file_data' check, because there might be a similar situation, but I can not prove it for the time being. Do you have any specific concerns about it?

> should be one of the 2 right? If that is the case, I suggest printing > "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. > The "test_sanity.c" is a module name, and the "test_no_static" is a static variable in this module. I just printed the debug info to help understand the current issue. In fact, the current issue happened in the productive environment, and the test module "test_sanity.c" is only used to help reproduce this issue. Hope this helps. Thanks Lianbo > Thanks, > 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 >