6 ms·

> Noncompliant, since `malloc(0)` is specified to return a unique pointer if it's not `NULL`. I know I've seen that somewhere, but may I ask what standard you'

> Noncompliant, since `malloc(0)` is specified to return a unique pointer if it's not `NULL`. I know I've seen that somewhere, but may I ask what standard you're referring to? If I recall correctly, this was an archaic stackless microcontroller. The heap support was mostly a marketing claim.

jmgao 1y ago
C89: https://port70.net/%7Ensz/c/c89/c89-draft.html https://port70.net/%7Ensz/c/c89/c89-draft.html If the size of the space requested is zero, the behavior is implementation-defined; the value returned shall be either a null pointer or a unique pointer.
- f1shy 1y ago
  Isn’t -1 basically 0xffff which is a constant pointer? What am I missinterpreting?
  - comex 1y ago
    If you call malloc(0) multiple times (without freeing in between) and get -1 each time, then the pointer is not unique.
    - deleted 1y ago
      [deleted]
    - bobmcnamara 1y ago
      But do we need a unique pointer or merely a pointer that is disjoint from all objects?
      - david-gpu 1y ago
        As per the specification, it has to be a unique pointer. Being tasked to implement a specification typically means having to pass extensive conformance tests and having to answer for instances of noncompliance. You soon learn to follow the spec to the letter, to the best of your abilities, unless you can make a strong case to your management for each specific deviation.
        magicalhippo 1y ago
        But the letter is non-specific. It doesn't clarify if unique refers to unique when compared to non-zero allocations, or unique when called multiple times. The C99 standard[1] seems to have worded it more precisely: If the size of the space requested is zero, the behavior is implementation- defined: either a null pointer is returned, or the behavior is as if the size were some nonzero value, except that the returned pointer shall not be used to access an object. [1]: https://rgambord.github.io/c99-doc/sections/7/20/3/index.html https://rgambord.github.io/c99-doc/sections/7/20/3/index.htm...
        bobmcnamara 1y ago
        It even replaced unique with "disjoint from any other object". -1 seems to be disjoint from all objects.
        magicalhippo 1y ago
        Sure, but always returning -1 would not satisfy "the behavior is as if the size were some nonzero value", as that would mean two consecutive calls to malloc(0) would return the same value. Which is not how malloc() with a non-zero size behaves per the previous part of the definition. Writing a specification is hard...
        f1shy 1y ago
        I think that is the problem. I understood unique as „only one“ which means always returns the same. It is imho not clear enough.
        minetest2048 1y ago
        This is embedded C where standard abuse is a thing: https://thephd.dev/conformance-should-mean-something-fputc-and-freestanding https://thephd.dev/conformance-should-mean-something-fputc-a...
        monobogdan 1y ago
        Hello! I'm sorry to bother you after 3 years of original comment: https://news.ycombinator.com/item?id=30738552 https://news.ycombinator.com/item?id=30738552 I have two questions: Could you please specify what have you meant by Fixed Function blocks on Adreno300+? Did you mean regular Rasterizer, DS and vertex assembler by this, or even portions of old FFP functionality just like lighting and etc from ES 1.x? Because I think there is no need in HW 1.x support, since even Samsung in their FIMG emulated most of classic FFP functionality like combiners through shades. I haven't investigated SGX53x drivers yet, but I think it was very same, since PVR MBX architecture was mostly abandoned in 2010. And second question: Why so many of early qcom android smartphones lacked GPU drivers at all? For example HTC Dream wasn't shipped with gpu drivers, as well as Magic and many Huawei models? For example, Moto droid has GPU drivers from the start.
      - comex 1y ago
        Well, sure, standards compliance doesn't matter much on such a small device. Personally I'd be less worried about uniqueness and more worried about alignment. An address of -1 would violate alignment requirements on most modern targets. But that may have been fine on the target in question; older microcontrollers tended to not have any hardware-level alignment requirements, and the C implementation could have treated all types as having alignment 1.
    - mystified5016 1y ago
      Null is not a unique pointer, it's a contant like -1 It returns multiple types of null pointer
      - comex 1y ago
        The spec says that malloc(0) shall return "either a null pointer or a unique pointer". If it's null, it doesn't have to be unique.
fredoralive 1y ago
Presumably the ANSI C standard or one of the later editions? They also cover the standard library as well as the language. (Presumably the bit about "Each such allocation shall yield a pointer to an object disjoint from any other object." if the random C99 draft I found via google is accurate to the final standard - I suppose you might question if this special use is technically an allocation of course). Of course, microcontrollers and the like can have somewhat eccentric implementations of languages of thing and perhaps aren't strictly compliant, and frankly even standard compliant stuff like "int can be 16 bits" might surprise some code that doesn't expect it.
o11c 1y ago
(you duped your comment under the other subthread) From C89, §7.10.3 "Memory management functions": > If the size of the space requested is > zero, the behavior is implementation-defined; the value returned shall be either a null pointer or a > unique pointer. The wording is different for C99 and POSIX, but I went back as far as possible (despite the poor source material; unlike later standards C89 is only accessible in scans and bad OCR, and also has catastrophic numbering differences). K&R C specifies nothing (it's often quite useless; people didn't actually write against K&R C but against the common subset of extensions of platforms they cared about), but its example implementation adds a block header without checking for 0 so it ends up doing the "unique non-NULL pointer" thing.
- bobmcnamara 1y ago
  I meant to ask both people the same question. I wouldn't be surprised if Win3.1-looking tool chain had not implemented c89, though I'm certain it wasn't c99 compliant, which only requires that the pointer is a disjoint from any object, not unique. It's strange that the standard has relaxed over time.

jmgao 1y ago

C89: https://port70.net/%7Ensz/c/c89/c89-draft.html https://port70.net/%7Ensz/c/c89/c89-draft.html If the size of the space requested is zero, the behavior is implementation-defined; the value returned shall be either a null pointer or a unique pointer.

f1shy 1y ago
Isn’t -1 basically 0xffff which is a constant pointer? What am I missinterpreting?
- comex 1y ago
  If you call malloc(0) multiple times (without freeing in between) and get -1 each time, then the pointer is not unique.
  - deleted 1y ago
    [deleted]
  - bobmcnamara 1y ago
    But do we need a unique pointer or merely a pointer that is disjoint from all objects?
    - david-gpu 1y ago
      As per the specification, it has to be a unique pointer. Being tasked to implement a specification typically means having to pass extensive conformance tests and having to answer for instances of noncompliance. You soon learn to follow the spec to the letter, to the best of your abilities, unless you can make a strong case to your management for each specific deviation.
      - magicalhippo 1y ago
        But the letter is non-specific. It doesn't clarify if unique refers to unique when compared to non-zero allocations, or unique when called multiple times. The C99 standard[1] seems to have worded it more precisely: If the size of the space requested is zero, the behavior is implementation- defined: either a null pointer is returned, or the behavior is as if the size were some nonzero value, except that the returned pointer shall not be used to access an object. [1]: https://rgambord.github.io/c99-doc/sections/7/20/3/index.html https://rgambord.github.io/c99-doc/sections/7/20/3/index.htm...
        bobmcnamara 1y ago
        It even replaced unique with "disjoint from any other object". -1 seems to be disjoint from all objects.
        magicalhippo 1y ago
        Sure, but always returning -1 would not satisfy "the behavior is as if the size were some nonzero value", as that would mean two consecutive calls to malloc(0) would return the same value. Which is not how malloc() with a non-zero size behaves per the previous part of the definition. Writing a specification is hard...
        f1shy 1y ago
        I think that is the problem. I understood unique as „only one“ which means always returns the same. It is imho not clear enough.
      - minetest2048 1y ago
        This is embedded C where standard abuse is a thing: https://thephd.dev/conformance-should-mean-something-fputc-and-freestanding https://thephd.dev/conformance-should-mean-something-fputc-a...
      - monobogdan 1y ago
        Hello! I'm sorry to bother you after 3 years of original comment: https://news.ycombinator.com/item?id=30738552 https://news.ycombinator.com/item?id=30738552 I have two questions: Could you please specify what have you meant by Fixed Function blocks on Adreno300+? Did you mean regular Rasterizer, DS and vertex assembler by this, or even portions of old FFP functionality just like lighting and etc from ES 1.x? Because I think there is no need in HW 1.x support, since even Samsung in their FIMG emulated most of classic FFP functionality like combiners through shades. I haven't investigated SGX53x drivers yet, but I think it was very same, since PVR MBX architecture was mostly abandoned in 2010. And second question: Why so many of early qcom android smartphones lacked GPU drivers at all? For example HTC Dream wasn't shipped with gpu drivers, as well as Magic and many Huawei models? For example, Moto droid has GPU drivers from the start.
    - comex 1y ago
      Well, sure, standards compliance doesn't matter much on such a small device. Personally I'd be less worried about uniqueness and more worried about alignment. An address of -1 would violate alignment requirements on most modern targets. But that may have been fine on the target in question; older microcontrollers tended to not have any hardware-level alignment requirements, and the C implementation could have treated all types as having alignment 1.
  - mystified5016 1y ago
    Null is not a unique pointer, it's a contant like -1 It returns multiple types of null pointer
    - comex 1y ago
      The spec says that malloc(0) shall return "either a null pointer or a unique pointer". If it's null, it doesn't have to be unique.

fredoralive 1y ago

Presumably the ANSI C standard or one of the later editions? They also cover the standard library as well as the language. (Presumably the bit about "Each such allocation shall yield a pointer to an object disjoint from any other object." if the random C99 draft I found via google is accurate to the final standard - I suppose you might question if this special use is technically an allocation of course). Of course, microcontrollers and the like can have somewhat eccentric implementations of languages of thing and perhaps aren't strictly compliant, and frankly even standard compliant stuff like "int can be 16 bits" might surprise some code that doesn't expect it.

o11c 1y ago

(you duped your comment under the other subthread) From C89, §7.10.3 "Memory management functions": > If the size of the space requested is > zero, the behavior is implementation-defined; the value returned shall be either a null pointer or a > unique pointer. The wording is different for C99 and POSIX, but I went back as far as possible (despite the poor source material; unlike later standards C89 is only accessible in scans and bad OCR, and also has catastrophic numbering differences). K&R C specifies nothing (it's often quite useless; people didn't actually write against K&R C but against the common subset of extensions of platforms they cared about), but its example implementation adds a block header without checking for 0 so it ends up doing the "unique non-NULL pointer" thing.

bobmcnamara 1y ago
I meant to ask both people the same question. I wouldn't be surprised if Win3.1-looking tool chain had not implemented c89, though I'm certain it wasn't c99 compliant, which only requires that the pointer is a disjoint from any object, not unique. It's strange that the standard has relaxed over time.