From: "Martin Storsjö" <martin@martin.st>
To: Nick Clifton <nickc@redhat.com>
Cc: binutils@sourceware.org
Subject: Re: [PATCH] ld: pe: Improve performance of object file exclude symbol directives
Date: Tue, 6 Sep 2022 12:39:50 +0300 (EEST) [thread overview]
Message-ID: <10615ade-446f-a711-ee6c-789a9d95ee57@martin.st> (raw)
In-Reply-To: <174963e9-fa71-b70e-7659-0f534db073f8@redhat.com>
On Mon, 5 Sep 2022, Nick Clifton wrote:
> Hi Martin,
>
>> Store the list of excluded symbols in a sorted list, speeding up
>> checking for duplicates when inserting new entries.
>
> An excellent idea.
FWIW, regarding most of this review here: This file already has got two
copies of the exact same routines for inserting structs into a sorted list
of structs (find_export_in_list, def_file_add_export, find_import_in_list,
def_file_add_import), so for this patch I just made a third copy of the
same routines, with the exact same behaviours, but adapted for the
exclude_symbol structs.
I'd be happy to adjust things based on your review, but then I'll probably
follow up with a separate patch to adapt the other existing
implementations based on this feedback.
>
>> /* From EXCLUDE_SYMBOLS or embedded directives. */
>> + int num_exclude_symbols;
>
> Presumably there can never be a negative number of excluded symbols,
> so using "unsigned int" here might be more appropriate.
Sure, I can change that.
>
>
>> + if (fdef->exclude_symbols)
>
> Given that the for() loop to follow checks fdef->num_exclude_symbols,
> this if() statement is redundant.
Sure, I can remove it. (The existing exports/imports lists of structs have
the exact same structure.)
>> + for (i = 0; i < fdef->num_exclude_symbols; i++)
>> + free (fdef->exclude_symbols[i].symbol_name);
>> + free (fdef->exclude_symbols);
>
> Calling free(NULL) is allowed, so the if() statement is still not needed.
Sure. (Also preexisting from exports/imports.)
>> +/* Search the position of the identical element, or returns the position
>> + of the next higher element. If last valid element is smaller, then MAX
>> + is returned. */
>
> The comment should explain the use of the IS_IDENT parameter.
>
> It should probably also note that MAX is expected to be the same as the
> number
> of entries in the B array.
Ok, I can expand the comment to explain these.
>> +static int
>> +find_exclude_in_list (def_file_exclude_symbol *b, int max,
>> + const char *name, int *is_ident)
>
> Since we are dealing with array indicies here, I would suggest that the
> function
> should return an unsigned int. Likewise the MAX parameter should be
> unsigned.
> Plus is_ident should be a boolean pointer, not an integer pointer.
Ok, I can change that. (Ditto for the preexisting functions.)
>
>> +static def_file_exclude_symbol *
>> +def_file_add_exclude_symbol (def_file *fdef, const char *name, int
>> *is_dup)
>
> I think that IS_DUP should be a "boolean *" not a "int *".
Ok
>
>> + int max_exclude_symbols = ROUND_UP(fdef->num_exclude_symbols, 32);
>
> Magic numbers are bad. Please replace 32 with a defined constant.
>
>> + if (fdef->num_exclude_symbols >= max_exclude_symbols)
>
> This is sneaky and not very intuitive. I would prefer it if you had
> two fields in the fdef structure, one for the number of allocated
> slots in the exclude_symbols array and one for the number of used slots.
>
> Then testing for when the array needs to be extended would be a case
> of comparing these two fields. Using two fields might take up more
> space in the structure, but it sure makes a lot more sense to me.
This was also designed according to the existing code - but yes, I agree
that using a separate variable keeping track of the allocation is much
safer and clearer. (It took a while to think through to see how this works
for the initial allocation and all that.)
>> + max_exclude_symbols = ROUND_UP(fdef->num_exclude_symbols + 1, 32);
>
> Given that the point of this patch is to improve performance when there
> are a large number of excluded symbols, incrementing the array by 32 slots
> at a time seems counter intuitive. I would suggest a bigger number, eg 1024
> or 10240.
Sure, or doubling as Jan suggested.
>> + e = fdef->exclude_symbols + pos;
>> + if (pos != fdef->num_exclude_symbols)
>> + memmove (&e[1], e, (sizeof (def_file_exclude_symbol) *
>> (fdef->num_exclude_symbols - pos)));
>
> What the ? OK, so what is going on here ? At the very least I think that
> you are going to need to add a comment to this piece of code.
Sure. (This is also preexisting code for the other lists.) As this inserts
into a sorted list of structs, it moves the later structs forward when
inserting in the middle of the list.
// Martin
prev parent reply other threads:[~2022-09-06 9:39 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-02 10:59 Martin Storsjö
2022-09-05 12:54 ` Nick Clifton
2022-09-06 7:40 ` Jan Beulich
2022-09-06 11:42 ` Nick Clifton
2022-09-06 11:54 ` Jan Beulich
2022-09-06 11:59 ` Martin Storsjö
2022-09-06 13:06 ` Nick Clifton
2022-09-06 9:39 ` Martin Storsjö [this message]
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