Re: [PATCH v2] gdb::handle_eintr, remove need to specify return type

Kamil Rytarowski
2020-10-13T14:58:13Z

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On 13.10.2020 16:17, Pedro Alves wrote:
> On 10/13/20 2:43 PM, Kamil Rytarowski wrote:
>
>> This patch applied on trunk gives me:
>>
>> gmake[2]: Wejście do katalogu '/public/binutils-gdb-netbsd/build/gdbserver'
>> CXX netbsd-low.o
>> ../../gdbserver/netbsd-low.cc: In function ‘bool elf_64_file_p(const
>> char*)’:
>> ../../gdbserver/netbsd-low.cc:1152:57: error: no matching function for
>> call to ‘handle_eintr(int, int (&)(const char*, int, ...), const char*&,
>> int)’
>> 1152 | int fd = gdb::handle_eintr (-1, ::open, file, O_RDONLY);
>> | ^
>> In file included from ../../gdbserver/netbsd-low.cc:37:
>> ../../gdbserver/../gdbsupport/eintr.h:58:1: note: candidate:
>> ‘template<class ErrorValType, class Fun, class ... Args> typename
>> gdb::return_type<Fun>::type gdb::handle_eintr(ErrorValType, const Fun&,
>> const Args& ...)’
>> 58 | handle_eintr (ErrorValType errval, const Fun &f, const Args &...
>> args)
>> | ^~~~~~~~~~~~
>> ../../gdbserver/../gdbsupport/eintr.h:58:1: note: template argument
>> deduction/substitution failed:
>> ../../gdbserver/../gdbsupport/eintr.h: In substitution of
>> ‘template<class ErrorValType, class Fun, class ... Args> typename
>> gdb::return_type<Fun>::type gdb::handle_eintr(ErrorValType, const Fun&,
>> const Args& ...) [with ErrorValType = int; Fun = int(const char*, int,
>> ...); Args = {const char*, int}]’:
>> ../../gdbserver/netbsd-low.cc:1152:57: required from here
>> ../../gdbserver/../gdbsupport/eintr.h:58:1: error: invalid use of
>> incomplete type ‘struct gdb::return_type<int(const char*, int, ...)>’
>> In file included from ../../gdbserver/../gdbsupport/poison.h:23,
>> from ../../gdbserver/../gdbsupport/common-utils.h:26,
>> from ../../gdbserver/../gdbsupport/common-defs.h:125,
>> from ../../gdbserver/server.h:22,
>> from ../../gdbserver/netbsd-low.cc:18:
>> ../../gdbserver/../gdbsupport/traits.h:49:8: note: declaration of
>> ‘struct gdb::return_type<int(const char*, int, ...)>’
>> 49 | struct return_type;
>> | ^~~~~~~~~~~
>
> Huh, Fun is clearly a function, yet the compiler doesn't pick
> the partial specialization.
>
> I could reproduce it here, seems to be related to open being varargs.
>
> Anyhow, we don't really need the new trait. We can just
> use decltype and a trailing return. I don't know why I didn't
> think of it in the first place.
>
> Here's an updated patch. I believe this one should work for you too.
>

This version works for me.

>
> From 37d06f47a379e44a895f68a22cbb0f745da33ec5 Mon Sep 17 00:00:00 2001
> From: Pedro Alves <pedro@palves.net>
> Date: Tue, 8 Sep 2020 17:34:41 +0100
> Subject: [PATCH v2] gdb::handle_eintr, remove need to specify return type
>
> This eliminates the need to specify the return type when using
> handle_eintr. We let the compiler deduce it for us.
>
> Also, use lowercase for function parameter names. Uppercase should
> only be used on template parameters.
>
> gdb/ChangeLog:
>
> * nat/linux-waitpid.c: Include "gdbsupport/eintr.h".
> (my_waitpid): Use gdb::handle_eintr.
>
> gdbserver/ChangeLog:
>
> * netbsd-low.cc (netbsd_waitpid, netbsd_process_target::kill)
> (netbsd_qxfer_libraries_svr4): Use gdb::handle_eintr without
> explicit type.
>
> gdbsupport/ChangeLog:
>
> * eintr.h (handle_eintr): Replace Ret template parameter with
> ErrorValType. Use it as type of the failure value. Deduce the
> function's return type using decltype. Use lowercase for function
> parameter names.
> ---
> gdb/nat/linux-waitpid.c | 11 ++---------
> gdbserver/netbsd-low.cc | 10 +++++-----
> gdbsupport/eintr.h | 32 +++++++++++++++++++-------------
> 3 files changed, 26 insertions(+), 27 deletions(-)
>
> diff --git a/gdb/nat/linux-waitpid.c b/gdb/nat/linux-waitpid.c
> index f50e0c7bcff..d066239220a 100644
> --- a/gdb/nat/linux-waitpid.c
> +++ b/gdb/nat/linux-waitpid.c
> @@ -22,6 +22,7 @@
> #include "linux-nat.h"
> #include "linux-waitpid.h"
> #include "gdbsupport/gdb_wait.h"
> +#include "gdbsupport/eintr.h"
>
> /* Convert wait status STATUS to a string. Used for printing debug
> messages only. */
> @@ -54,13 +55,5 @@ status_to_str (int status)
> int
> my_waitpid (int pid, int *status, int flags)
> {
> - int ret;
> -
> - do
> - {
> - ret = waitpid (pid, status, flags);
> - }
> - while (ret == -1 && errno == EINTR);
> -
> - return ret;
> + return gdb::handle_eintr (-1, ::waitpid, pid, status, flags);
> }
> diff --git a/gdbserver/netbsd-low.cc b/gdbserver/netbsd-low.cc
> index 30028d3a384..519614d0473 100644
> --- a/gdbserver/netbsd-low.cc
> +++ b/gdbserver/netbsd-low.cc
> @@ -245,7 +245,7 @@ netbsd_waitpid (ptid_t ptid, struct target_waitstatus *ourstatus,
> int options = (target_options & TARGET_WNOHANG) ? WNOHANG : 0;
>
> pid_t pid
> - = gdb::handle_eintr<int> (-1, ::waitpid, ptid.pid (), &status, options);
> + = gdb::handle_eintr (-1, ::waitpid, ptid.pid (), &status, options);
>
> if (pid == -1)
> perror_with_name (_("Child process unexpectedly missing"));
> @@ -456,7 +456,7 @@ netbsd_process_target::kill (process_info *process)
> return -1;
>
> int status;
> - if (gdb::handle_eintr<int> (-1, ::waitpid, pid, &status, 0) == -1)
> + if (gdb::handle_eintr (-1, ::waitpid, pid, &status, 0) == -1)
> return -1;
> mourn (process);
> return 0;
> @@ -1149,15 +1149,15 @@ netbsd_qxfer_libraries_svr4 (const pid_t pid, const char *annex,
> static bool
> elf_64_file_p (const char *file)
> {
> - int fd = gdb::handle_eintr<int> (-1, ::open, file, O_RDONLY);
> + int fd = gdb::handle_eintr (-1, ::open, file, O_RDONLY);
> if (fd < 0)
> perror_with_name (("open"));
>
> Elf64_Ehdr header;
> - ssize_t ret = gdb::handle_eintr<ssize_t> (-1, ::read, fd, &header, sizeof (header));
> + ssize_t ret = gdb::handle_eintr (-1, ::read, fd, &header, sizeof (header));
> if (ret == -1)
> perror_with_name (("read"));
> - gdb::handle_eintr<int> (-1, ::close, fd);
> + gdb::handle_eintr (-1, ::close, fd);
> if (ret != sizeof (header))
> error ("Cannot read ELF file header: %s", file);
>
> diff --git a/gdbsupport/eintr.h b/gdbsupport/eintr.h
> index 64ff5940b75..02c26e4def1 100644
> --- a/gdbsupport/eintr.h
> +++ b/gdbsupport/eintr.h
> @@ -43,25 +43,31 @@ namespace gdb
>
> You could wrap it by writing the wrapped form:
>
> - ssize_t ret = gdb::handle_eintr<ssize_t> (-1, ::write, pipe[1], "+", 1);
> -
> - The RET typename specifies the return type of the wrapped system call, which
> - is typically int or ssize_t. The R argument specifies the failure value
> - indicating the interrupted syscall when calling the F function with
> - the A... arguments. */
> -
> -template <typename Ret, typename Fun, typename... Args>
> -inline Ret handle_eintr (const Ret &R, const Fun &F, const Args &... A)
> + ssize_t ret = gdb::handle_eintr (-1, ::write, pipe[1], "+", 1);
> +
> + ERRVAL specifies the failure value indicating that the call to the
> + F function with ARGS... arguments was possibly interrupted with a
> + signal. */
> +
> +template <typename ErrorValType,
> + typename Fun,
> + typename... Args>
> +inline auto
> +handle_eintr (ErrorValType errval, const Fun &f, const Args &... args)
> + -> decltype (f(args...))
> {
> - Ret ret;
> + decltype (f(args...)) ret;
> +
> do
> {
> errno = 0;
> - ret = F (A...);
> + ret = f (args...);
> }
> - while (ret == R && errno == EINTR);
> + while (ret == errval && errno == EINTR);
> +
> return ret;
> }
> -}
> +
> +} /* namespace gdb */
>
> #endif /* GDBSUPPORT_EINTR_H */
>
> base-commit: 87a37e5e078f506fa9905b74e9238593c537fcd5
>

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