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Comments (7)

Alogani avatar Alogani commented on July 22, 2024 1

How could it ?

Example 1:

include mycustomSigaction

var a = Sigaction()
a.sa_handler = proc(x: cint) {.noconv.} = echo "catch", x

Output:

Error: undeclared field: 'sa_handler=' for type in.Sigaction [type declared in /usercode/in.nim(9, 6)]

Example 2:

include mycustomSigaction

var a = Sigaction()
a.internal.sa_handler = proc(x: cint) {.noconv.} = echo "catch", x

Output:

In file included from /usercode/nimcache/@min.nim.c:8:
/usercode/nimcache/@min.nim.c:43:40: error: expected ':', ',', ';', '}' or '__attribute__' before '.' token
   43 |         tyProc__KdSUXb6rBxR37qf0lYK7pQ sa_handler;
      |                                        ^~~~~~~~~~
/usercode/nimcache/@min.nim.c: In function 'NimMainModule':
/usercode/nimcache/@min.nim.c:172:50: error: 'struct sigaction' has no member named 'internal'
  172 |         nimlf_(15, "/usercode/in.nim"); a__in_u17.internal.sa_handler = colonanonymous___in_u18;
      |

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litlighilit avatar litlighilit commented on July 22, 2024 1

Have you tested it ? ^^

I really didn't...

as in my current linux machine, the union is defined as an anonymous union...

It's really another big problem that different posix has different name for definition.

Okey, in C sa_hander is defined as a macro1 to something like __sigaction_handler.sa_handler to support writing C code like s.sa_hanler,

therefore the sa_handler symbol is just polluted, leading code above no working.

For this case (and in fact for many other), such a workaround is invalid.

Footnotes

  1. in fact in Nim we are using the similiar mechanism (via template/proc as getter/setter), but thanks to it that Nim's template can be typed and more flexible, such a problem won't be caused in Nim. ↩

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litlighilit avatar litlighilit commented on July 22, 2024

Why

type Sigaction_internal {.union.} = object
    sa_handler*: proc (x: cint) {.noconv.}
    sa_sigaction*: proc (x: cint, y: ptr SigInfo, z: pointer) {.noconv.}

type Sigaction* {.importc: "struct sigaction", header: "<signal.h>", final, pure.} = object
    internal: Sigaction_internal
    sa_mask*: Sigset
    sa_flags*: cint

not working?

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litlighilit avatar litlighilit commented on July 22, 2024

I didn't realize it until now that

Nim's offsetof is also mapped to C's operator.

The field access is mapped to C's too, instead of accessing via calculated offset, which is what I used to think.

Then I just cannot give a real-world example where the fields' order of a imported struct or whether they contains union matters.

e.g. Even though in my system, Uid is of wrong size, (shall be 4, but 8 in Nim), nowadays, the code used to cause bug now works fine... (may because Nim used to calculate size itself, but now it uses C's sizeof)

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Alogani avatar Alogani commented on July 22, 2024

@litlighilit don't know about future development on Nim's NIR or nlvm project. But if Nim's import are close to C definitions, this will make life easier on future. But I don't know more than you do

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litlighilit avatar litlighilit commented on July 22, 2024
For this case, there is a solution: 
type Sigaction_internal {.union.} = object
    sa_handler*: proc (x: cint) {.noconv.}
    sa_sigaction*: proc (x: cint, y: ptr SigInfo, z: pointer) {.noconv.}

type Sigaction* {.importc: "struct sigaction", header: "<signal.h>", final, pure.} = object
    internal{.importc: "__sigaction_u".}: Sigaction_internal
    sa_mask*: Sigset
    sa_flags*: cint

But when it comes to anonymous union, there may be really no support yet...

So the {.union.}: ... pragma statement can be introduced to solve this, but it shall be for anonymous union only.

Edit: not working for this case, see below for details.

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Alogani avatar Alogani commented on July 22, 2024

Have you tested it ? ^^

type Sigset* {.importc: "sigset_t", header: "<signal.h>", final, pure.} = object
    abi: array[1024 div (8 * sizeof(culong)), culong]

type Sigaction_internal {.union.} = object
    sa_handler*: proc (x: cint) {.noconv.}
    sa_sigaction*: proc (x: cint, y: pointer, z: pointer) {.noconv.}

type Sigaction* {.importc: "struct sigaction", header: "<signal.h>", final, pure.} = object
    internal{.importc: "__sigaction_u".}: Sigaction_internal
    sa_mask*: Sigset
    sa_flags*: cint

var a = Sigaction()
a.internal.sa_handler = proc(x: cint) {.noconv.} = echo "catch", x

Output

Hint: used config file '/playground/nim/config/nim.cfg' [Conf]
Hint: used config file '/playground/nim/config/config.nims' [Conf]
......................................................................
Hint: gcc -c  -w -fmax-errors=3 -pthread   -I/playground/nim/lib -I/usercode -o /usercode/nimcache/@m..@splayground@snim@slib@[email protected] /usercode/nimcache/@m..@splayground@snim@slib@[email protected] [Exec]
Hint: gcc -c  -w -fmax-errors=3 -pthread   -I/playground/nim/lib -I/usercode -o /usercode/nimcache/@m..@splayground@snim@slib@sstd@[email protected] /usercode/nimcache/@m..@splayground@snim@slib@sstd@[email protected] [Exec]
Hint: gcc -c  -w -fmax-errors=3 -pthread   -I/playground/nim/lib -I/usercode -o /usercode/nimcache/@m..@splayground@snim@slib@[email protected] /usercode/nimcache/@m..@splayground@snim@slib@[email protected] [Exec]
Hint: gcc -c  -w -fmax-errors=3 -pthread   -I/playground/nim/lib -I/usercode -o /usercode/nimcache/@m..@splayground@snim@[email protected] /usercode/nimcache/@m..@splayground@snim@[email protected] [Exec]
Hint: gcc -c  -w -fmax-errors=3 -pthread   -I/playground/nim/lib -I/usercode -o /usercode/nimcache/@min.nim.c.o /usercode/nimcache/@min.nim.c [Exec]
In file included from /usercode/nimcache/@min.nim.c:8:
/usercode/nimcache/@min.nim.c:42:40: error: expected ':', ',', ';', '}' or '__attribute__' before '.' token
   42 |         tyProc__KdSUXb6rBxR37qf0lYK7pQ sa_handler;
      |                                        ^~~~~~~~~~
/usercode/nimcache/@min.nim.c: In function 'NimMainModule':
/usercode/nimcache/@min.nim.c:171:50: error: 'struct sigaction' has no member named '__sigaction_u'
  171 |         nimlf_(14, "/usercode/in.nim"); a__in_u16.__sigaction_u.sa_handler = colonanonymous___in_u17;
      |

And even if it worked, having to do a.internal.sa_handler whereas in c, it is a.sa_handler is a problematic workaround IMHO

from nim.

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