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More UB madness from LLVM/Clang
Via @johnregehr this further tale of compiler “optimizations” that break correct C code without even a warning by deleting a necessary null pointer check. In this example, Bar contains a stack of...
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Pointer alias analysis in C
Perhaps there is some reason to provide a mechanism for asserting, in a particular patch of code, that the compiler is free to make optimistic assumptions about the kinds of aliasing that can occur. I...
View ArticleTorvalds on aliasing
See also pointer alias in C and Depressing and faintly terrifying days for the C standard. From: LKML From Linus Torvalds <> Date Tue, 5 Jun 2018 10:30:21 -0700 Subject Re: [GIT PULL] Device...
View ArticleThree modest proposals for the C standard WG14
1. Proposal on Undefined Behavior. Rationale: This Standard definition of “undefined behavior”, like the rest of the Standard, relies on an implicit expectation that implementations are cooperating...
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Spanner in the works
The developers of Google’s Spanner database built an interesting system but chose to build their own clock synchronization technology instead of getting a more precise off the shelf solution and chose...
View ArticleThe C Standard and GCC/Clang are an active safety and security danger
Code controlling a device – a medical instrument, a power plant, an airplane, perfectly working and thoroughly tested code can be turned into garbage if someone runs a new version of a C compiler or...
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undefined behavior and the purpose of C
The C programming language, by design, permits programmers to work at both low and high level. In particular, for applications like operating system development, cryptography, numerical methods, and...
View ArticleVector optimization with C aliasing
One of the common defenses of the abuse of “undefined behavior” by C compilers, and the stupid aliasing rules in the standard is that those things are necessary for optimizations, like using vector...
View ArticlePractical uses of synchronized clocks -Liskov
From 1991, Barbara Liskov looked at the implications for distributed computing when synchronized clocks are available. PracticalUseOfClocks
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Semiotics of functional programming
In contrast to the usual imperative languages (e.g., C, Fortran, and Ada), in which variables represent cells in memory that can be modified using the assignment operator = (or :=), functional...
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Concurrency
\(\newcommand{\ess}{Initial} \) Michel Charpentier provides a nice example of a simple, flawed, producer/consumer buffer implementation. The fundamental problem could be discovered by doing a Stack...
View ArticleDepressing and faintly terrifying days for the C standard
C STANDARD UNDEFINED BEHAVIOR VERSUS WITTGENSTEIN 1. DEPRESSING AND FAINTLY TERRIFYING Chris Lattner, the architect of the Clang/LLVM C compiler explained the effects of the C standard’s “undefined...
View ArticleC89 Standard
A text version of a non-final draft is below. Here’s the pdf of the final version. (This foreword is not a part of American National Standard for Information Systems --- Programming Language C,...
View ArticleDennis Ritchie on alias analysis in the C programming language 1988
This 1998 note by Dennis Ritchie from comp.lang.c (and also here ) is very current since the concept of noalias has definitely crept back into the standard. I have reproduced it verbatim, but lightly...
View ArticleC is not a serious programming language
The C Standards process over the last few decades has addressed both optimization and pointer type safety largely through a concept called “undefined behavior”. The idea is that instead of positive...
View ArticleUndefined behavior in C is a reading error.
Considering how important “undefined behavior” has become to C semantics and the ISO/IEC JTC1/SC22/WG14 Committee, the lack of any reference to it in the K&R ANSI book is notable and the...
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Dissing the PDP11
In computer science academia, C along with UNIX, and PDP11s, is as unfashionable as can be: the equivalent of other 1970’s relics, like polyester leisure suits and mullets. In 2018 ACM Queue published...
View ArticleMemory model and semantics for C
A perceptive note from Linus Torvalds about the C/C++ “memory model” is reproduced below. From Linus Torvalds <> Date Thu, 7 Jun 2018 08:40:49 -0700 Subject Re: LKMM litmus test for Roman...
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