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

Yao Qi
2017-02-07T10:54:17Z

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 (é½å°§)

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;
}