[Xen-devel] [PATCH v4 20/34] x86, xsplice: Print payload's symbol name and payload name in backtraces

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

From: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>

Naturally the backtrace is presented when an instruction
hits an bug_frame or %p is used.

The payloads do not support bug_frames yet - however the functions
the payloads call could hit an BUG() or WARN().
The traps.c has logic to scan for it this - and eventually it will
find the correct bug_frame and the walk the stack using %p to print
the backtrace. For %p and symbols to print a string -  the
'is_active_kernel_text' is consulted which uses an 'struct virtual_region'.

Therefore we register our start->end addresses so that
'is_active_kernel_text' will include our payload address.

We also register our symbol lookup table function so that it can
scan the list of payloads and retrieve the correct name.

Lastly we change vsprintf to take into account s and namebuf.
For core code they are the same, but for payloads they are different.
This gets us:

Xen call trace:
   [<ffff82d080a00041>] revert_hook+0x31/0x35 [xen_hello_world]
   [<ffff82d0801431bd>] xsplice.c#revert_payload+0x86/0xc6
   [<ffff82d080143502>] check_for_xsplice_work+0x233/0x3cd
   [<ffff82d08017a0b2>] domain.c#continue_idle_domain+0x9/0x1f

Which is great if payloads have similar or same symbol names.

Signed-off-by: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>

---
Cc: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
Cc: Jan Beulich <jbeulich@xxxxxxxx>
Cc: Keir Fraser <keir@xxxxxxx>
Cc: Tim Deegan <tim@xxxxxxx>

v2: Add missing full stop.
v3: s/module/payload/
v4: Expand comment and include registration of 'virtual_region'
v5: Redo the vsprintf handling of payload name.
---
 xen/common/vsprintf.c | 15 +++++++++---
 xen/common/xsplice.c  | 67 ++++++++++++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 78 insertions(+), 4 deletions(-)

diff --git a/xen/common/vsprintf.c b/xen/common/vsprintf.c
index 18d2634..f0b743f 100644
--- a/xen/common/vsprintf.c
+++ b/xen/common/vsprintf.c
@@ -20,6 +20,7 @@
 #include <xen/symbols.h>
 #include <xen/lib.h>
 #include <xen/sched.h>
+#include <xen/xsplice.h>
 #include <asm/div64.h>
 #include <asm/page.h>
 
@@ -331,16 +332,17 @@ static char *pointer(char *str, char *end, const char 
**fmt_ptr,
     {
         unsigned long sym_size, sym_offset;
         char namebuf[KSYM_NAME_LEN+1];
+        bool_t payload = 0;
 
         /* Advance parents fmt string, as we have consumed 's' or 'S' */
         ++*fmt_ptr;
 
         s = symbols_lookup((unsigned long)arg, &sym_size, &sym_offset, 
namebuf);
-
-        /* If the symbol is not found, fall back to printing the address */
+        /* If the symbol is not found, fall back to printing the address. */
         if ( !s )
             break;
-
+        if ( strncmp(namebuf, s, KSYM_NAME_LEN) )
+            payload = 1;
         /* Print symbol name */
         str = string(str, end, s, -1, -1, 0);
 
@@ -354,6 +356,13 @@ static char *pointer(char *str, char *end, const char 
**fmt_ptr,
             str = number(str, end, sym_size, 16, -1, -1, SPECIAL);
         }
 
+        if ( payload )
+        {
+            str = string(str, end, " [", -1, -1, 0);
+            str = string(str, end, namebuf, -1, -1, 0);
+            str = string(str, end, "]", -1, -1, 0);
+        }
+
         return str;
     }
 
diff --git a/xen/common/xsplice.c b/xen/common/xsplice.c
index 54120bb..a3366ef 100644
--- a/xen/common/xsplice.c
+++ b/xen/common/xsplice.c
@@ -3,6 +3,7 @@
  *
  */
 
+#include <xen/bug_ex_symbols.h>
 #include <xen/cpu.h>
 #include <xen/guest_access.h>
 #include <xen/keyhandler.h>
@@ -13,6 +14,7 @@
 #include <xen/smp.h>
 #include <xen/softirq.h>
 #include <xen/spinlock.h>
+#include <xen/string.h>
 #include <xen/symbols.h>
 #include <xen/vmap.h>
 #include <xen/wait.h>
@@ -50,6 +52,7 @@ struct payload {
     struct list_head applied_list;       /* Linked to 'applied_list'. */
     struct xsplice_patch_func *funcs;    /* The array of functions to patch. */
     unsigned int nfuncs;                 /* Nr of functions to patch. */
+    struct virtual_region bug_ex_region; /*.bug.frame patching and exception 
table. */
     struct xsplice_symbol *symtab;       /* All symbols. */
     char *strtab;                        /* Pointer to .strtab. */
     unsigned int nsyms;                  /* Nr of entries in .strtab and 
symbols. */
@@ -103,6 +106,12 @@ static int verify_payload(const 
xen_sysctl_xsplice_upload_t *upload)
     return 0;
 }
 
+static bool_t ignore_region(unsigned int flag, unsigned long priv)
+{
+    /* See CHECKING_[SYMBOL|BUG_FRAME|EXCEPTION]. */
+    return !(flag & priv);
+}
+
 uint64_t xsplice_symbols_lookup_by_name(const char *symname)
 {
     struct payload *data;
@@ -131,6 +140,51 @@ out:
     return value;
 }
 
+static const char *xsplice_symbols_lookup(unsigned long addr,
+                                          unsigned long *symbolsize,
+                                          unsigned long *offset,
+                                          char *namebuf)
+{
+    struct payload *data;
+    unsigned int i;
+    int best;
+
+    /*
+     * No locking since this list is only ever changed during apply or revert
+     * context.
+     */
+    list_for_each_entry ( data, &applied_list, applied_list )
+    {
+        if ( !((void *)addr >= data->payload_address &&
+               (void *)addr < (data->payload_address + data->core_text_size)) )
+            continue;
+
+        best = -1;
+
+        for ( i = 0; i < data->nsyms; i++ )
+        {
+            if ( data->symtab[i].value <= addr &&
+                 ( best == -1 ||
+                   data->symtab[best].value < data->symtab[i].value) )
+                best = i;
+        }
+
+        if ( best == -1 )
+            return NULL;
+
+        if ( symbolsize )
+            *symbolsize = data->symtab[best].size;
+        if ( offset )
+            *offset = addr - data->symtab[best].value;
+        if ( namebuf )
+            strlcpy(namebuf, data->name, KSYM_NAME_LEN);
+
+        return data->symtab[best].name;
+    }
+
+    return NULL;
+}
+
 static int find_payload(const xen_xsplice_name_t *name, struct payload **f)
 {
     struct payload *data;
@@ -325,6 +379,7 @@ static int prepare_payload(struct payload *payload,
     struct xsplice_elf_sec *sec;
     unsigned int i;
     struct xsplice_patch_func *f;
+    struct virtual_region *region;
 
     sec = xsplice_elf_sec_by_name(elf, ".xsplice.funcs");
     if ( sec )
@@ -377,6 +432,15 @@ static int prepare_payload(struct payload *payload,
                    XSPLICE, elf->name, f->name, f->old_addr);
         }
     }
+
+    /* Setup the virtual region with proper data. */
+    region = &payload->bug_ex_region;
+    region->skip = ignore_region;
+    region->symbols_lookup = xsplice_symbols_lookup;
+    region->priv = CHECKING_SYMBOL;
+    region->start = (unsigned long)payload->payload_address;
+    region->end = (unsigned long)(payload->payload_address + 
payload->core_text_size);
+
     return 0;
 }
 
@@ -479,7 +543,6 @@ static int build_symbol_table(struct payload *payload,
     payload->symtab = symtab;
     payload->strtab = strtab;
     payload->nsyms = nsyms;
-
     return 0;
 }
 
@@ -707,6 +770,7 @@ static int apply_payload(struct payload *data)
     arch_xsplice_patching_leave();
 
     list_add_tail(&data->applied_list, &applied_list);
+    register_virtual_region(&data->bug_ex_region);
 
     return 0;
 }
@@ -729,6 +793,7 @@ static int revert_payload(struct payload *data)
     arch_xsplice_patching_leave();
 
     list_del_init(&data->applied_list);
+    unregister_virtual_region(&data->bug_ex_region);
 
     return 0;
 }
-- 
2.5.0


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