Re: [RFC 3/7] Add basic Linux kernel support

[Yao Qi <qiyaoltc@gmail.com>]

On 17-01-12 12:32:13, Philipp Rudo wrote:
>     (ALL_TARGET_OBS): Add lk-low.o

ALL_TARGET_OBS is used with --enable-targets=all, so if we put lk-low.o
in it, lk-low.o can't be linked into GDB if we don't enable all targets.

>     (COMMON_OBS): Add lk-lists.o
> ---

> +
> +/* Initialize a private data entry for an address, where NAME is the name
> +   of the symbol, i.e. variable name in Linux, ALIAS the name used to
> +   retrieve the entry from hashtab, and SILENT a flag to determine if
> +   errors should be ignored.
> +
> +   Returns a pointer to the new entry.  In case of an error, either returns
> +   NULL (SILENT = TRUE) or throws an error (SILENT = FALSE).  If SILENT = TRUE
> +   the caller is responsible to check for errors.
> +
> +   Do not use directly, use LK_DECLARE_* macros defined in lk-low.h instead.  */
> +
> +struct lk_private_data *
> +lk_init_addr (const char *name, const char *alias, int silent)
> +{
> +  /* Initialize to NULL to silence gcc.  */
> +  struct value *val = NULL;
> +  struct lk_private_data *data;
> +  void **new_slot;
> +  void *old_slot;
> +
> +  if ((old_slot = lk_find (alias)) != NULL)
> +    return (struct lk_private_data *) old_slot;
> +
> +  TRY
> +    {
> +      /* Choose global block for search, in case the variable was redefined
> +	 in the current context.  */
> +      const struct block *global = block_global_block (get_selected_block (0));
> +      const char *tmp = name;
> +      expression_up expr = parse_exp_1 (&tmp, 0, global, 0);

Why don't you look up symbol or msymbol?  like Peter's patch does.

> +
> +      gdb_assert (*tmp == '\0');
> +      val = evaluate_expression (expr.get ());
> +    }
> +  CATCH (except, RETURN_MASK_ALL)
> +    {
> +      if (!silent)
> +	error (_("Could not find address %s. Abort."), alias);
> +
> +      return NULL;
> +    }
> +  END_CATCH
> +
> +  data = XCNEW (struct lk_private_data);
> +  data->alias = alias;
> +  data->data.addr = value_address (val);
> +
> +  new_slot = lk_find_slot (alias);
> +  *new_slot = data;
> +
> +  return data;
> +}
> +
> +/* Same as lk_init_addr but for structs.  */
> +
> +struct lk_private_data *
> +lk_init_struct (const char *name, const char *alias, int silent)
> +{
> +  /* Initialize to NULL to silence GCC.  */
> +  struct value *val = NULL;
> +  struct lk_private_data *data;
> +  void **new_slot;
> +  void *old_slot;
> +
> +  if ((old_slot = lk_find (alias)) != NULL)
> +    return (struct lk_private_data *) old_slot;
> +
> +  /* There are two ways to define structs
> +	o struct name { ... };
> +	o typedef struct { ... } name;
> +    Both are used in the linux kernel.  Thus we have to check for both ways.
> +    We do this by first searching for "struct name" (the "struct " is added
> +    by macro LK_STRUCT_NAME in lk-low.h) and if not found seach for "name".
> +
> +    Note: The alias will always keep its "struct "-prefix, even when
> +    given explicitely. Besides some weird error messages this has no effect.
> +  */
> +retry:
> +  TRY
> +    {
> +      /* Choose global block for search, in case the struct was redefined
> +	 in the current context.  */
> +      const struct block *global = block_global_block(get_selected_block (0));
> +      const char *tmp = name;
> +      expression_up expr = parse_exp_1 (&tmp, 0, global, 0);

Likewise.

> +
> +      gdb_assert (*tmp == '\0');
> +      /* parsing just for 'name' can cause name clashes.  Thus also check for
> +	 OP_TYPE.  */
> +      if (expr->elts[0].opcode != OP_TYPE)
> +	    error ("We just need to get to the catch block");
> +
> +      val = evaluate_type (expr.get ());
> +    }
> +  CATCH (except, RETURN_MASK_ALL)
> +    {
> +      /* 7 = strlen ("struct ").  */
> +      if (strncmp (name, "struct ", 7) == 0)
> +	{
> +	  name += 7;
> +	  goto retry;
> +	}
> +
> +      if (!silent)
> +	error (_("Could not find %s. Abort."), alias);
> +
> +      return NULL;
> +    }
> +  END_CATCH
> +
> +  data = XCNEW (struct lk_private_data);
> +  data->alias = alias;
> +  data->data.type = value_type (val);
> +
> +  new_slot = lk_find_slot (alias);
> +  *new_slot = data;
> +
> +  return data;
> +}
> +

I am playing your first three patches on x86_64 with some hacks.
I write a small program with the same linux kernel "signature", and
want GDB treat it as a linux kernel.

(gdb) b main
Breakpoint 1 at 0x4004fa: file /home/yao/SourceCode/gnu/gdb/git/gdb/testsuite/gdb.base/linux-kernel.c, line 59.
(gdb) run
Starting program: /scratch/yao/gdb/build-git/x86_64/gdb/testsuite/outputs/gdb.base/linux-kernel/linux-kernel
Could not map thread with pid 28278, lwp 28278 to a cpu.

I hope we can have a small test case in gdb testsuite to test linux
kernel debugging.  Is it possible?  We can generate a normal coredump
to linux-kernel in test, and we can also set up task_struct and expect
GDB sees some "threads".  What do you think?

-- 
Yao (齐尧)


static char linux_banner[10];
static int _stext = 0;
static int _etext = 0;

typedef int pid_t;

struct list_head
{
  struct list_head *next, *prev;
};

struct thread_struct
{};

struct task_struct
{
  struct list_head tasks;
  pid_t pid;
  pid_t tgid;
  struct list_head thread_group;
  char comm[20];

  struct thread_struct thread;
};

struct rq
{
  struct task_struct *curr;
};

#define DIV_ROUND_UP(n, d) (((n) + (d) - 1) / (d))
#define BITS_PER_BYTE           8
#define BITS_TO_LONGS(nr)       DIV_ROUND_UP(nr, BITS_PER_BYTE * sizeof(long))

#define DECLARE_BITMAP(name,bits) \
  unsigned long name[BITS_TO_LONGS(bits)]

#define NR_CPUS 10

struct cpumask { DECLARE_BITMAP(bits, NR_CPUS); };

struct cpumask __cpu_online_mask;

struct task_struct init_task;
struct rq runqueues;
struct cpumask baz;

unsigned long __per_cpu_offset[NR_CPUS];

struct mm_struct
{};

struct mm_struct init_mm;

int
main (void)
{
  return 0;
}