3 ms·

It would be nice to have a code snippet for each of the examples. I'm a fairly experienced C++ developer but my knowledge of compilers is, admittedly, lacking

• pixdamix 15y ago
  There's this patch from the linux-kernel: - http://lkml.org/lkml/2009/7/17/187 http://lkml.org/lkml/2009/7/17/187 - http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=a3ca86aea507904148870946d599e07a340b39bf http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6... I've put a gist file demonstrating the problem: https://gist.github.com/968723 https://gist.github.com/968723 #include <stdio.h> struct agnx_priv { char demo; }; struct ieee80211_hw { struct agnx_priv *priv; }; struct pci_dev { struct ieee80211_hw* dev; }; struct ieee80211_hw* pci_get_drvdata(struct pci_dev *pdev) { if(!pdev) return NULL; return pdev->dev; } static void agnx_pci_remove (struct pci_dev *pdev) { struct ieee80211_hw *dev = pci_get_drvdata(pdev); struct agnx_priv *priv = dev->priv; if (!dev) return; // This will segfault if the previous if is optimized printf("%c\n", priv->demo); } int main(int argc, char **argv) { // (struct pci_dev *)argv[1] is just to avoid compiler optimisations // =~ NULL if no args are passed. struct pci_dev * pdev = (struct pci_dev *)argv[1]; agnx_pci_remove(pdev); return 0; } Compile with: gcc -O2 -ggdb -Wall -Wundef -fno-strict-aliasing \ -fno-common -fdelete-null-pointer-checks test-deref.c \ -o test-deref and gcc -O2 -ggdb -Wall -Wundef -fno-strict-aliasing \ -fno-common -fno-delete-null-pointer-checks test-deref.c \ -o test-deref