[v2] gdbserver: Check r_version < 1 for Linux debugger interface
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Commit Message
Update gdbserver to check r_version < 1 instead of r_version != 1 so
that r_version can be bumped for a new field in the glibc debugger
interface to support multiple namespaces. Since so far, the gdbserver
only reads fields defined for r_version == 1, it is compatible with
r_version >= 1.
All future glibc debugger interface changes will be backward compatible.
If there is ever the need for backward incompatible change to the glibc
debugger interface, a new DT_XXX element will be provided to access the
new incompatible interface.
PR gdb/11839
* linux-low.cc (linux_process_target::qxfer_libraries_svr4):
Check r_version < 1 instead of r_version != 1.
---
gdbserver/linux-low.cc | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
Comments
On Mon, Aug 16, 2021 at 1:30 PM H.J. Lu <hjl.tools@gmail.com> wrote:
>
> Update gdbserver to check r_version < 1 instead of r_version != 1 so
> that r_version can be bumped for a new field in the glibc debugger
> interface to support multiple namespaces. Since so far, the gdbserver
> only reads fields defined for r_version == 1, it is compatible with
> r_version >= 1.
>
> All future glibc debugger interface changes will be backward compatible.
> If there is ever the need for backward incompatible change to the glibc
> debugger interface, a new DT_XXX element will be provided to access the
> new incompatible interface.
>
> PR gdb/11839
> * linux-low.cc (linux_process_target::qxfer_libraries_svr4):
> Check r_version < 1 instead of r_version != 1.
> ---
> gdbserver/linux-low.cc | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/gdbserver/linux-low.cc b/gdbserver/linux-low.cc
> index 5c6191d941c..fc7a995351d 100644
> --- a/gdbserver/linux-low.cc
> +++ b/gdbserver/linux-low.cc
> @@ -6845,7 +6845,7 @@ linux_process_target::qxfer_libraries_svr4 (const char *annex,
> if (linux_read_memory (priv->r_debug + lmo->r_version_offset,
> (unsigned char *) &r_version,
> sizeof (r_version)) != 0
> - || r_version != 1)
> + || r_version < 1)
> {
> warning ("unexpected r_debug version %d", r_version);
> }
> --
> 2.31.1
>
Set r_version == 2 breaks GDB due to
static CORE_ADDR
solib_svr4_r_ldsomap (struct svr4_info *info)
{
struct link_map_offsets *lmo = svr4_fetch_link_map_offsets ();
struct type *ptr_type = builtin_type (target_gdbarch ())->builtin_data_ptr;
enum bfd_endian byte_order = type_byte_order (ptr_type);
ULONGEST version = 0;
try
{
/* Check version, and return zero if `struct r_debug' doesn't have
the r_ldsomap member. */
version
= read_memory_unsigned_integer (info->debug_base +
lmo->r_version_offset,
lmo->r_version_size, byte_order);
}
catch (const gdb_exception_error &ex)
{
exception_print (gdb_stderr, ex);
}
if (version < 2 || lmo->r_ldsomap_offset == -1)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
glibc doesn't have r_ldsomap. But r_ldsomap_offset is set
unconditionally. Shouldn't it be set only if the target debugger
interface has it?
return 0;
return read_memory_typed_address (info->debug_base + lmo->r_ldsomap_offset,
ptr_type);
}
On Mon, Aug 16, 2021 at 3:02 PM H.J. Lu <hjl.tools@gmail.com> wrote:
>
> On Mon, Aug 16, 2021 at 1:30 PM H.J. Lu <hjl.tools@gmail.com> wrote:
> >
> > Update gdbserver to check r_version < 1 instead of r_version != 1 so
> > that r_version can be bumped for a new field in the glibc debugger
> > interface to support multiple namespaces. Since so far, the gdbserver
> > only reads fields defined for r_version == 1, it is compatible with
> > r_version >= 1.
> >
> > All future glibc debugger interface changes will be backward compatible.
> > If there is ever the need for backward incompatible change to the glibc
> > debugger interface, a new DT_XXX element will be provided to access the
> > new incompatible interface.
> >
> > PR gdb/11839
> > * linux-low.cc (linux_process_target::qxfer_libraries_svr4):
> > Check r_version < 1 instead of r_version != 1.
> > ---
> > gdbserver/linux-low.cc | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/gdbserver/linux-low.cc b/gdbserver/linux-low.cc
> > index 5c6191d941c..fc7a995351d 100644
> > --- a/gdbserver/linux-low.cc
> > +++ b/gdbserver/linux-low.cc
> > @@ -6845,7 +6845,7 @@ linux_process_target::qxfer_libraries_svr4 (const char *annex,
> > if (linux_read_memory (priv->r_debug + lmo->r_version_offset,
> > (unsigned char *) &r_version,
> > sizeof (r_version)) != 0
> > - || r_version != 1)
> > + || r_version < 1)
> > {
> > warning ("unexpected r_debug version %d", r_version);
> > }
> > --
> > 2.31.1
> >
>
> Set r_version == 2 breaks GDB due to
>
> static CORE_ADDR
> solib_svr4_r_ldsomap (struct svr4_info *info)
> {
> struct link_map_offsets *lmo = svr4_fetch_link_map_offsets ();
> struct type *ptr_type = builtin_type (target_gdbarch ())->builtin_data_ptr;
> enum bfd_endian byte_order = type_byte_order (ptr_type);
> ULONGEST version = 0;
>
> try
> {
> /* Check version, and return zero if `struct r_debug' doesn't have
> the r_ldsomap member. */
> version
> = read_memory_unsigned_integer (info->debug_base +
> lmo->r_version_offset,
> lmo->r_version_size, byte_order);
> }
> catch (const gdb_exception_error &ex)
> {
> exception_print (gdb_stderr, ex);
> }
>
> if (version < 2 || lmo->r_ldsomap_offset == -1)
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>
> glibc doesn't have r_ldsomap. But r_ldsomap_offset is set
> unconditionally. Shouldn't it be set only if the target debugger
> interface has it?
>
> return 0;
>
> return read_memory_typed_address (info->debug_base + lmo->r_ldsomap_offset,
> ptr_type);
> }
>
I opened:
https://sourceware.org/bugzilla/show_bug.cgi?id=28236
On 2021-08-16 4:30 p.m., H.J. Lu wrote:
> Update gdbserver to check r_version < 1 instead of r_version != 1 so
> that r_version can be bumped for a new field in the glibc debugger
> interface to support multiple namespaces. Since so far, the gdbserver
> only reads fields defined for r_version == 1, it is compatible with
> r_version >= 1.
>
> All future glibc debugger interface changes will be backward compatible.
> If there is ever the need for backward incompatible change to the glibc
> debugger interface, a new DT_XXX element will be provided to access the
> new incompatible interface.
>
> PR gdb/11839
> * linux-low.cc (linux_process_target::qxfer_libraries_svr4):
> Check r_version < 1 instead of r_version != 1.
Note that GDB doesn't use ChangeLogs. You can use
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=11839
To link to the Bugzilla entry.
> ---
> gdbserver/linux-low.cc | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/gdbserver/linux-low.cc b/gdbserver/linux-low.cc
> index 5c6191d941c..fc7a995351d 100644
> --- a/gdbserver/linux-low.cc
> +++ b/gdbserver/linux-low.cc
> @@ -6845,7 +6845,7 @@ linux_process_target::qxfer_libraries_svr4 (const char *annex,
> if (linux_read_memory (priv->r_debug + lmo->r_version_offset,
> (unsigned char *) &r_version,
> sizeof (r_version)) != 0
> - || r_version != 1)
> + || r_version < 1)
This patch LGTM. As you noted, things break when bumping r_version to 2
because of r_ldsomap, but since there isn't a glibc out there using
r_version == 2, I think that this patch can safely go in right now.
Simon
On 2021-08-16 6:02 p.m., H.J. Lu wrote:
> On Mon, Aug 16, 2021 at 1:30 PM H.J. Lu <hjl.tools@gmail.com> wrote:
>>
>> Update gdbserver to check r_version < 1 instead of r_version != 1 so
>> that r_version can be bumped for a new field in the glibc debugger
>> interface to support multiple namespaces. Since so far, the gdbserver
>> only reads fields defined for r_version == 1, it is compatible with
>> r_version >= 1.
>>
>> All future glibc debugger interface changes will be backward compatible.
>> If there is ever the need for backward incompatible change to the glibc
>> debugger interface, a new DT_XXX element will be provided to access the
>> new incompatible interface.
>>
>> PR gdb/11839
>> * linux-low.cc (linux_process_target::qxfer_libraries_svr4):
>> Check r_version < 1 instead of r_version != 1.
>> ---
>> gdbserver/linux-low.cc | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/gdbserver/linux-low.cc b/gdbserver/linux-low.cc
>> index 5c6191d941c..fc7a995351d 100644
>> --- a/gdbserver/linux-low.cc
>> +++ b/gdbserver/linux-low.cc
>> @@ -6845,7 +6845,7 @@ linux_process_target::qxfer_libraries_svr4 (const char *annex,
>> if (linux_read_memory (priv->r_debug + lmo->r_version_offset,
>> (unsigned char *) &r_version,
>> sizeof (r_version)) != 0
>> - || r_version != 1)
>> + || r_version < 1)
>> {
>> warning ("unexpected r_debug version %d", r_version);
>> }
>> --
>> 2.31.1
>>
>
> Set r_version == 2 breaks GDB due to
>
> static CORE_ADDR
> solib_svr4_r_ldsomap (struct svr4_info *info)
> {
> struct link_map_offsets *lmo = svr4_fetch_link_map_offsets ();
> struct type *ptr_type = builtin_type (target_gdbarch ())->builtin_data_ptr;
> enum bfd_endian byte_order = type_byte_order (ptr_type);
> ULONGEST version = 0;
>
> try
> {
> /* Check version, and return zero if `struct r_debug' doesn't have
> the r_ldsomap member. */
> version
> = read_memory_unsigned_integer (info->debug_base +
> lmo->r_version_offset,
> lmo->r_version_size, byte_order);
> }
> catch (const gdb_exception_error &ex)
> {
> exception_print (gdb_stderr, ex);
> }
>
> if (version < 2 || lmo->r_ldsomap_offset == -1)
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>
> glibc doesn't have r_ldsomap. But r_ldsomap_offset is set
> unconditionally. Shouldn't it be set only if the target debugger
> interface has it?
Ideally, I think that Solaris support would implement its own
"solaris_{ilp32,lp64}_fetch_link_map_offsets", where it would set
r_ldsomap_offset. And either there wouldn't be a generic
svr4_{ilp32,lp64}_fetch_link_map_offsets (each OS support would provide
its own, because things vary so much between OSes) or
svr4_{ilp32,lp64}_fetch_link_map_offsets would just specify what's
really the common denominator between all of them.
I think that would allow remove that "version < 2" check that is a bit
ugly.
Simon
* H. J. Lu via Gdb-patches:
> Set r_version == 2 breaks GDB due to
>
> static CORE_ADDR
> solib_svr4_r_ldsomap (struct svr4_info *info)
> {
> struct link_map_offsets *lmo = svr4_fetch_link_map_offsets ();
> struct type *ptr_type = builtin_type (target_gdbarch ())->builtin_data_ptr;
> enum bfd_endian byte_order = type_byte_order (ptr_type);
> ULONGEST version = 0;
>
> try
> {
> /* Check version, and return zero if `struct r_debug' doesn't have
> the r_ldsomap member. */
> version
> = read_memory_unsigned_integer (info->debug_base +
> lmo->r_version_offset,
> lmo->r_version_size, byte_order);
> }
> catch (const gdb_exception_error &ex)
> {
> exception_print (gdb_stderr, ex);
> }
>
> if (version < 2 || lmo->r_ldsomap_offset == -1)
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>
> glibc doesn't have r_ldsomap. But r_ldsomap_offset is set
> unconditionally. Shouldn't it be set only if the target debugger
> interface has it?
glibc should add r_ldsomap_offset and switch its own version number to
3, I think.
Thanks,
Florian
On Tue, Aug 17, 2021 at 6:48 AM Florian Weimer <fweimer@redhat.com> wrote:
>
> * H. J. Lu via Gdb-patches:
>
> > Set r_version == 2 breaks GDB due to
> >
> > static CORE_ADDR
> > solib_svr4_r_ldsomap (struct svr4_info *info)
> > {
> > struct link_map_offsets *lmo = svr4_fetch_link_map_offsets ();
> > struct type *ptr_type = builtin_type (target_gdbarch ())->builtin_data_ptr;
> > enum bfd_endian byte_order = type_byte_order (ptr_type);
> > ULONGEST version = 0;
> >
> > try
> > {
> > /* Check version, and return zero if `struct r_debug' doesn't have
> > the r_ldsomap member. */
> > version
> > = read_memory_unsigned_integer (info->debug_base +
> > lmo->r_version_offset,
> > lmo->r_version_size, byte_order);
> > }
> > catch (const gdb_exception_error &ex)
> > {
> > exception_print (gdb_stderr, ex);
> > }
> >
> > if (version < 2 || lmo->r_ldsomap_offset == -1)
> > ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> >
> > glibc doesn't have r_ldsomap. But r_ldsomap_offset is set
> > unconditionally. Shouldn't it be set only if the target debugger
> > interface has it?
>
> glibc should add r_ldsomap_offset and switch its own version number to
> 3, I think.
We can add an OS flavor field to struct link_map_offsets for this.
@@ -6845,7 +6845,7 @@ linux_process_target::qxfer_libraries_svr4 (const char *annex,
if (linux_read_memory (priv->r_debug + lmo->r_version_offset,
(unsigned char *) &r_version,
sizeof (r_version)) != 0
- || r_version != 1)
+ || r_version < 1)
{
warning ("unexpected r_debug version %d", r_version);
}